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())