Fix API endpoint configuration and domain references

- Change NEXT_PUBLIC_ENTE_ENDPOINT to relative /api for domain flexibility
- Remove runtime JS endpoint replacement (fragile, now unnecessary)
- Fix all domain references to use CLOUDRON_APP_DOMAIN consistently
- Add /ping health check endpoint to Caddy configuration
- Update placeholder server to use dynamic domain

Photos app now working, other apps may need additional fixes.

Dockerfile

@@ -28,10 +28,10 @@ RUN apt-get update && apt-get install -y git && \
 RUN corepack enable
 
 # Set environment variables for web app build
-# Set the API endpoint to use current origin - this will work at runtime
-ENV NEXT_PUBLIC_ENTE_ENDPOINT="https://example.com/api"
+# Use relative API endpoint so it works with any domain
+ENV NEXT_PUBLIC_ENTE_ENDPOINT="/api"
 # Add a note for clarity
-RUN echo "Building with placeholder NEXT_PUBLIC_ENTE_ENDPOINT, will be served by Caddy proxy at /api"
+RUN echo "Building with relative NEXT_PUBLIC_ENTE_ENDPOINT=/api, will be served by Caddy proxy"
 
 # Debugging the repository structure
 RUN find . -type d -maxdepth 3 | sort