fix: production deployment issues with Traefik and database migrations

- Add missing created_at column to email_queue table
- Fix 502 Bad Gateway errors with proper Traefik routing configuration
- Create docker-compose.traefik.yml for external Traefik deployment
- Fix health check endpoint path for API path stripping
- Add PostgreSQL init script for Umami database creation
- Add comprehensive deployment guide for Traefik setup

The backend now properly handles /api prefix stripping by Traefik and
migrations run safely in production environments with existing schemas.

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

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

docker/postgres-init/01-create-umami-db.sql

@@ -0,0 +1,8 @@
+-- Create umami database if it doesn't exist
+-- This runs as the postgres superuser during initialization
+
+SELECT 'CREATE DATABASE umami'
+WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'umami')\gexec
+
+-- Grant all privileges on umami database to the application user
+GRANT ALL PRIVILEGES ON DATABASE umami TO "${POSTGRES_USER}";