fix: resolve critical production deployment issues

- Fix database connection error "getaddrinfo ENOTFOUND postgres"
- Add wait-for-db.sh script to ensure PostgreSQL is ready before starting
- Fix email processor initialization timing issue
- Add missing storage path environment variables
- Add database dependency to backend service
- Enhance health check endpoint with database connectivity check
- Update production database defaults to match docker-compose
- Install postgresql-client in Docker image for health checks
- Document all required environment variables in .env.example

Fixes immediate production deployment failures and ensures proper service startup order.

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

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

docker-compose.prod.yml

@@ -8,6 +8,8 @@ services:
       context: ./backend
       dockerfile: Dockerfile
     restart: unless-stopped
+    depends_on:
+      - db
     environment:
       - NODE_ENV=production
       - PORT=3000
@@ -31,6 +33,10 @@ services:
       # Analytics
       - UMAMI_URL=${UMAMI_URL}
       - UMAMI_WEBSITE_ID=${UMAMI_WEBSITE_ID}
+      # Storage paths
+      - STORAGE_PATH=/app/storage
+      - EVENTS_PATH=/app/storage/events
+      - ARCHIVE_PATH=/app/storage/events/archived
     volumes:
       - ./storage:/app/storage
       - ./data:/app/data