Fix web app endpoint configuration

- Use relative /api endpoint in Dockerfile build
- Remove complex runtime replacement logic
- Simplify start.sh to avoid read-only filesystem issues
- Restore working Caddy configuration

Version 0.1.78 ready for deployment

CloudronManifest.json

@@ -7,7 +7,7 @@
   "contactEmail": "contact@ente.io",
   "tagline": "Open Source End-to-End Encrypted Photos & Authentication",
   "upstreamVersion": "1.0.0",
-  "version": "0.1.69",
+  "version": "0.1.78",
   "healthCheckPath": "/ping",
   "httpPort": 3080,
   "memoryLimit": 1073741824,