Fix static asset routing for all web apps

- Add specific _next asset routes for accounts, auth, cast apps
- Add image asset routes for each app
- Ensure each app's assets are served from correct directory
- Keep photos app routing unchanged

Should fix accounts/auth/cast apps loading issues.

CloudronManifest.json

@@ -7,7 +7,7 @@
   "contactEmail": "contact@ente.io",
   "tagline": "Open Source End-to-End Encrypted Photos & Authentication",
   "upstreamVersion": "1.0.0",
-  "version": "0.1.79",
+  "version": "0.1.80",
   "healthCheckPath": "/ping",
   "httpPort": 3080,
   "memoryLimit": 1073741824,