chore(docker): update ports and switch frontend to serve static files

- Change frontend port from 80 to 8847 and backend port from 3001 to 9173 in .env.example
- Replace nginx stage in frontend Dockerfile with node alpine and serve for static hosting
- Remove nginx.conf and related configuration for frontend static serving
- Update docker-compose ports and healthcheck URLs to match new port assignments
- Adjust server Dockerfile to expose new backend port 9173 and update healthcheck URL
- Create non-root user in frontend Dockerfile and run serve command on port 8847
- Update healthcheck commands to use wget on new ports for both frontend and backend

.env.example

@@ -29,8 +29,8 @@ REDIRECT_URI=http://localhost:5173/auth/callback
 # ======================
 # Ports (Coolify will override these)
 # ======================
-FRONTEND_PORT=80
-BACKEND_PORT=3001
+FRONTEND_PORT=8847
+BACKEND_PORT=9173
 
 # ======================
 # Environment