Improve URL replacement strategy for frontend assets

- Enhanced rewrite_frontend_reference function to handle multiple URL encoding formats
- Now replaces plain URLs, backslash-escaped URLs, and double-backslash-escaped URLs
- Added https://ente.io -> BASE_URL replacement
- Version bump to 0.3.0

CloudronManifest.json

@@ -7,7 +7,7 @@
   "contactEmail": "contact@ente.io",
   "website": "https://ente.io",
   "tagline": "Open source, end-to-end encrypted photo backup",
-  "version": "0.2.2",
+  "version": "0.3.0",
   "upstreamVersion": "git-main",
   "healthCheckPath": "/health",
   "httpPort": 3080,