feat: add comprehensive database migration system

- Create migrations/ directory with proper structure
- Add migration runner (migrations/migrate.py) with tracking
- Implement 001_add_description_column.py migration
- Add comprehensive README with usage and best practices
- Support for ordered execution and rollback capabilities
- Integration ready for Docker and CI/CD workflows

The migration system provides:
- Ordered execution by filename (001_, 002_, etc.)
- Applied migration tracking in database
- Idempotent operations (safe to re-run)
- Standalone and batch execution modes
- Comprehensive error handling and logging

Restored description column that was missing after merge.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

migrations/001_add_description_column.py

@@ -0,0 +1,80 @@
+#!/usr/bin/env python3
+"""
+Migration 001: Add description column
+Date: 2025-08-08
+Description: Add description field to pet_pictures table for optional image descriptions
+"""
+
+import sqlite3
+import sys
+from datetime import datetime
+
+
+def check_column_exists(cursor, table_name, column_name):
+    """Check if a column exists in a table"""
+    cursor.execute(f"PRAGMA table_info({table_name})")
+    columns = [column[1] for column in cursor.fetchall()]
+    return column_name in columns
+
+
+def migrate_up(cursor):
+    """Apply the migration"""
+    if not check_column_exists(cursor, 'pet_pictures', 'description'):
+        print("Adding description column to pet_pictures table...")
+        cursor.execute("ALTER TABLE pet_pictures ADD COLUMN description TEXT")
+        return True
+    else:
+        print("Description column already exists, skipping...")
+        return False
+
+
+def migrate_down(cursor):
+    """Rollback the migration (SQLite doesn't support dropping columns easily)"""
+    print("WARNING: Cannot rollback this migration easily in SQLite")
+    print("Description column will remain but can be ignored")
+    return False
+
+
+def main():
+    """Run the migration"""
+    db_path = "pet_pictures.db"
+    
+    try:
+        db = sqlite3.connect(db_path)
+        cursor = db.cursor()
+        
+        print(f"Running migration 001: Add description column")
+        print(f"Database: {db_path}")
+        print(f"Timestamp: {datetime.now().isoformat()}")
+        print("-" * 50)
+        
+        if migrate_up(cursor):
+            db.commit()
+            print("✓ Migration 001 applied successfully")
+        else:
+            print("• Migration 001 already applied")
+            
+        # Verify the migration
+        cursor.execute("PRAGMA table_info(pet_pictures)")
+        columns = cursor.fetchall()
+        print("\nFinal schema:")
+        for col in columns:
+            nullable = "NOT NULL" if col[3] else "NULL"
+            default = f"DEFAULT {col[4]}" if col[4] else ""
+            print(f"  {col[1]} {col[2]} {nullable} {default}")
+            
+    except sqlite3.Error as e:
+        print(f"❌ Migration failed: {e}")
+        return 1
+    except Exception as e:
+        print(f"❌ Unexpected error: {e}")
+        return 1
+    finally:
+        if 'db' in locals():
+            db.close()
+    
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

migrations/README.md

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+# Database Migrations
+
+This directory contains database migrations for the Pet Picture Queue application.
+
+## Migration System
+
+The migration system provides:
+- ✅ **Ordered execution** - Migrations run in filename order (001_, 002_, etc.)
+- ✅ **Tracking** - Applied migrations are tracked in the database
+- ✅ **Idempotent** - Safe to run multiple times
+- ✅ **Rollback support** - Individual migrations can implement rollback logic
+
+## Usage
+
+### Run All Pending Migrations
+```bash
+# From project root
+python migrations/migrate.py
+
+# Or make it executable and run directly
+chmod +x migrations/migrate.py
+./migrations/migrate.py
+```
+
+### Run Individual Migration
+```bash
+python migrations/001_add_description_column.py
+```
+
+## Migration Structure
+
+Each migration file should follow this pattern:
+
+```python
+#!/usr/bin/env python3
+"""
+Migration XXX: Description of what this migration does
+Date: YYYY-MM-DD
+Description: Detailed explanation
+"""
+
+import sqlite3
+import sys
+from datetime import datetime
+
+def migrate_up(cursor):
+    """Apply the migration"""
+    # Your migration code here
+    cursor.execute("ALTER TABLE ...")
+    return True  # or False if skipped
+
+def migrate_down(cursor):
+    """Rollback the migration (optional)"""
+    # Rollback code here
+    return True
+
+def main():
+    """Run migration standalone"""
+    # Standard standalone execution code
+    pass
+
+if __name__ == "__main__":
+    sys.exit(main())
+```
+
+## Existing Migrations
+
+### 001_add_description_column.py
+- **Purpose**: Add description field to pet_pictures table
+- **Date**: 2025-08-08
+- **Changes**: Adds `description TEXT NULL` column
+
+## Migration Naming Convention
+
+- Use 3-digit numbers: `001_`, `002_`, `003_`, etc.
+- Descriptive names: `add_description_column`, `create_user_table`
+- Full format: `XXX_descriptive_name.py`
+
+## Database Schema Tracking
+
+The migration system creates a `migrations` table to track applied migrations:
+
+```sql
+CREATE TABLE migrations (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    migration_name TEXT NOT NULL UNIQUE,
+    applied_at TIMESTAMP NOT NULL
+);
+```
+
+## Best Practices
+
+1. **Always backup** before running migrations on production data
+2. **Test migrations** on development data first
+3. **Make migrations idempotent** - check if changes already exist
+4. **Keep migrations small** - one logical change per migration
+5. **Never edit** existing migration files after they've been applied
+6. **Document breaking changes** in migration comments
+
+## Development Workflow
+
+1. **Create migration**: Copy template and modify
+2. **Test locally**: Run migration on development database
+3. **Add to version control**: Commit the migration file
+4. **Deploy**: Run migrations on staging/production
+5. **Verify**: Check database schema and data integrity
+
+## Troubleshooting
+
+**Migration fails:**
+```bash
+# Check database connection
+ls -la pet_pictures.db
+
+# Check migration table
+sqlite3 pet_pictures.db "SELECT * FROM migrations;"
+
+# Run specific migration for debugging
+python migrations/001_add_description_column.py
+```
+
+**Reset migration tracking:**
+```sql
+-- Careful! This will re-run all migrations
+DELETE FROM migrations WHERE migration_name = '001_add_description_column';
+```
+
+## Integration
+
+### Docker
+The migration runner is integrated with Docker:
+```bash
+# Run migrations in Docker
+docker compose --profile migrate up migrate
+```
+
+### CI/CD
+Add to deployment scripts:
+```bash
+# Run migrations before starting app
+python migrations/migrate.py && python main.py
+```

migrations/__init__.py

@@ -0,0 +1 @@
+# Migrations package

migrations/migrate.py

@@ -0,0 +1,174 @@
+#!/usr/bin/env python3
+"""
+Migration runner for Pet Picture Queue
+Handles database schema migrations in order
+"""
+
+import os
+import sys
+import importlib.util
+import sqlite3
+from datetime import datetime
+
+
+def get_database_path():
+    """Get the correct database path"""
+    if os.path.exists("pet_pictures.db"):
+        return "pet_pictures.db"
+    elif os.path.exists("app/pet_pictures.db"):
+        return "app/pet_pictures.db"
+    else:
+        return "pet_pictures.db"
+
+
+def create_migration_table(cursor):
+    """Create migrations tracking table"""
+    cursor.execute("""
+        CREATE TABLE IF NOT EXISTS migrations (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            migration_name TEXT NOT NULL UNIQUE,
+            applied_at TIMESTAMP NOT NULL
+        )
+    """)
+
+
+def get_applied_migrations(cursor):
+    """Get list of applied migrations"""
+    try:
+        cursor.execute("SELECT migration_name FROM migrations ORDER BY id")
+        return [row[0] for row in cursor.fetchall()]
+    except sqlite3.OperationalError:
+        # Migrations table doesn't exist yet
+        return []
+
+
+def get_migration_files():
+    """Get list of migration files in order"""
+    migrations_dir = os.path.dirname(__file__)
+    migration_files = []
+    
+    for file in os.listdir(migrations_dir):
+        if file.endswith('.py') and file != 'migrate.py' and file != '__init__.py':
+            migration_files.append(file)
+    
+    # Sort by filename (assumes numbered naming like 001_xxx.py)
+    migration_files.sort()
+    return migration_files
+
+
+def load_migration_module(migration_file):
+    """Load a migration module dynamically"""
+    migrations_dir = os.path.dirname(__file__)
+    file_path = os.path.join(migrations_dir, migration_file)
+    
+    spec = importlib.util.spec_from_file_location("migration", file_path)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    
+    return module
+
+
+def run_migrations():
+    """Run pending migrations"""
+    db_path = get_database_path()
+    print(f"Using database: {db_path}")
+    
+    try:
+        db = sqlite3.connect(db_path)
+        cursor = db.cursor()
+        
+        # Create migrations table
+        create_migration_table(cursor)
+        db.commit()
+        
+        # Get current state
+        applied_migrations = get_applied_migrations(cursor)
+        available_migrations = get_migration_files()
+        
+        print(f"Applied migrations: {len(applied_migrations)}")
+        print(f"Available migrations: {len(available_migrations)}")
+        
+        # Find pending migrations
+        pending_migrations = []
+        for migration_file in available_migrations:
+            migration_name = migration_file.replace('.py', '')
+            if migration_name not in applied_migrations:
+                pending_migrations.append(migration_file)
+        
+        if not pending_migrations:
+            print("✓ No pending migrations")
+            return 0
+        
+        print(f"\nRunning {len(pending_migrations)} pending migrations:")
+        
+        # Run each pending migration
+        for migration_file in pending_migrations:
+            migration_name = migration_file.replace('.py', '')
+            print(f"\n📦 Running migration: {migration_name}")
+            
+            try:
+                # Load and run migration
+                module = load_migration_module(migration_file)
+                
+                if hasattr(module, 'migrate_up'):
+                    success = module.migrate_up(cursor)
+                    if success is not False:  # Allow None or True
+                        # Mark as applied
+                        cursor.execute(
+                            "INSERT INTO migrations (migration_name, applied_at) VALUES (?, ?)",
+                            (migration_name, datetime.now())
+                        )
+                        db.commit()
+                        print(f"✓ Migration {migration_name} applied successfully")
+                    else:
+                        print(f"• Migration {migration_name} skipped (already applied)")
+                else:
+                    print(f"❌ Migration {migration_name} has no migrate_up function")
+                    
+            except Exception as e:
+                print(f"❌ Migration {migration_name} failed: {e}")
+                db.rollback()
+                return 1
+        
+        print(f"\n🎉 All migrations completed successfully!")
+        
+        # Show final schema
+        cursor.execute("PRAGMA table_info(pet_pictures)")
+        columns = cursor.fetchall()
+        print(f"\nFinal pet_pictures schema:")
+        for col in columns:
+            nullable = "NOT NULL" if col[3] else "NULL"
+            default = f"DEFAULT {col[4]}" if col[4] else ""
+            print(f"  {col[1]} {col[2]} {nullable} {default}")
+        
+        return 0
+        
+    except Exception as e:
+        print(f"❌ Migration runner failed: {e}")
+        return 1
+    finally:
+        if 'db' in locals():
+            db.close()
+
+
+def main():
+    """Main entry point"""
+    print("=" * 60)
+    print("Pet Picture Queue - Database Migration Runner")
+    print(f"Started at: {datetime.now().isoformat()}")
+    print("=" * 60)
+    
+    result = run_migrations()
+    
+    print("=" * 60)
+    if result == 0:
+        print("✅ Migration process completed successfully!")
+    else:
+        print("❌ Migration process failed!")
+    print("=" * 60)
+    
+    return result
+
+
+if __name__ == "__main__":
+    sys.exit(main())