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>

.env.example

@@ -0,0 +1,14 @@
+# Database Configuration
+DATABASE_URL=postgresql://yottob:yottob_password@postgres:5432/yottob
+
+# Celery Configuration
+CELERY_BROKER_URL=redis://redis:6379/0
+CELERY_RESULT_BACKEND=redis://redis:6379/0
+
+# Flask Configuration
+FLASK_ENV=development
+
+# PostgreSQL Configuration (for docker-compose)
+POSTGRES_USER=yottob
+POSTGRES_PASSWORD=yottob_password
+POSTGRES_DB=yottob