Migrate to Docker Compose with PostgreSQL

- Created docker-compose.yml with 4 services:
  - postgres: PostgreSQL 16 database with persistent volume
  - redis: Redis 7 message broker
  - app: Flask web application (port 5000)
  - celery: Celery worker for async downloads
- Created Dockerfile with Python 3.14, FFmpeg, and uv
- Added psycopg2-binary dependency for PostgreSQL driver
- Updated database.py to use DATABASE_URL environment variable
  - Supports PostgreSQL in production
  - Falls back to SQLite for local development
- Updated celery_app.py to use environment variables:
  - CELERY_BROKER_URL and CELERY_RESULT_BACKEND
- Created .env.example with all configuration variables
- Created .dockerignore to optimize Docker builds
- Updated .gitignore to exclude .env and Docker files
- Updated CLAUDE.md with comprehensive Docker documentation:
  - Quick start with docker-compose commands
  - Environment variable configuration
  - Local development setup instructions
  - Service architecture overview

All services have health checks and automatic restart configured.
Start entire stack with: docker-compose up

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

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

database.py

@@ -1,5 +1,6 @@
 """Database configuration and session management."""
 
+import os
 from contextlib import contextmanager
 from typing import Generator
 
@@ -9,15 +10,20 @@ from sqlalchemy.orm import sessionmaker, Session
 from models import Base
 
 
-# Database configuration
-DATABASE_URL = "sqlite:///yottob.db"
+# Database configuration from environment variable
+# Falls back to SQLite for local development if DATABASE_URL not set
+DATABASE_URL = os.getenv("DATABASE_URL", "sqlite:///yottob.db")
 
-# Create engine
-engine = create_engine(
-    DATABASE_URL,
-    echo=False,  # Set to True for SQL query logging
-    connect_args={"check_same_thread": False}  # Needed for SQLite
-)
+# Create engine with appropriate configuration
+engine_kwargs = {
+    "echo": False,  # Set to True for SQL query logging
+}
+
+# SQLite-specific configuration
+if DATABASE_URL.startswith("sqlite"):
+    engine_kwargs["connect_args"] = {"check_same_thread": False}
+
+engine = create_engine(DATABASE_URL, **engine_kwargs)
 
 # Session factory
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)