Add Traefik reverse proxy support with automatic SSL

Configure Immich to work with existing Traefik instance:
- Add Traefik labels to immich-server for automatic routing
- Add external traefik network connection
- Disable direct port exposure (use Traefik instead)
- Add DOMAIN variable to .env.example
- Improve .gitignore for generated files and volumes
- Add comprehensive README with deployment instructions

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitignore

@@ -1 +1,18 @@
+# Environment variables
 .env
+
+# Upload directory
+library/
+
+# Docker volumes
+pgdata/
+
+# System files
+.DS_Store
+Thumbs.db
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo