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

server/src/routes/oidc.js

@@ -196,7 +196,7 @@ router.get('/callback', async (req, res) => {
     // Generate JWT and redirect to frontend
     const token = generateToken(user);
     // In dev mode, frontend runs on a different port
-    res.redirect(frontendUrl(`/login?token=${token}`));
+    res.redirect(frontendUrl(`/login#token=${token}`));
   } catch (err) {
     console.error('[OIDC] Callback error:', err);
     res.redirect(frontendUrl('/login?oidc_error=server_error'));