Security hardening, backup restore fix & restore warning modal

- Fix backup restore: try/finally ensures DB always reopens after closeDb
- Fix EBUSY on uploads during restore (in-place overwrite instead of rmSync)
- Add DB proxy null guard for clearer errors during restore window
- Add red warning modal before backup restore (DE/EN, dark mode support)
- JWT secret: empty docker-compose default so auto-generation kicks in
- OIDC: pass token via URL fragment instead of query param (no server logs)
- Block SVG uploads on photos, files and covers (stored XSS prevention)
- Add helmet for security headers (HSTS, X-Frame, nosniff, etc.)
- Explicit express.json body size limit (100kb)
- Fix XSS in Leaflet map markers (escape image_url in HTML)
- Remove verbose WebSocket debug logging from client

docker-compose.yml

@@ -6,7 +6,7 @@ services:
       - "3000:3000"
     environment:
       - NODE_ENV=production
-      - JWT_SECRET=${JWT_SECRET:-change-me-to-a-long-random-string}
+      - JWT_SECRET=${JWT_SECRET:-}
       # - ALLOWED_ORIGINS=https://yourdomain.com  # Optional: restrict CORS to specific origins
       - PORT=3000
     volumes: