refactor: merge gateway functionality into frontend container

Eliminated duplicate nginx containers by merging gateway reverse proxy
functionality into the frontend container. This simplifies deployment
and reduces resource usage.

Architecture changes:
- Frontend now serves both static files AND reverse proxies to backend
- Single nginx container handles all HTTP routing
- Gateway container removed from builds and Helm chart

Dockerfile.frontend changes:
- Added upstream backend configuration
- Added proxy locations for /api, /health, /metrics, /npm, /pypi, /go, /ws
- Added rate limiting for API and downloads
- Added WebSocket support
- Configurable via BACKEND_HOST and BACKEND_PORT env vars

Helm chart changes:
- Updated frontend deployment to configure backend connection
- Simplified ingress to single route (all traffic → frontend)
- Frontend proxies backend requests internally
- Removed separate frontend/api ingress configurations

GoReleaser changes:
- Removed gohoarder-gateway Docker build
- Now builds: server, scanner, migrate, frontend (4 images)

Benefits:
- Fewer containers to manage
- Reduced complexity in Docker Compose and Kubernetes
- Single point of configuration for routing
- Better resource utilization

helm/gohoarder/values.yaml

@@ -507,21 +507,12 @@ ingress:
     nginx.ingress.kubernetes.io/proxy-read-timeout: "300"
     nginx.ingress.kubernetes.io/proxy-send-timeout: "300"
 
-  # Ingress for frontend
-  frontend:
-    enabled: true
-    host: "gohoarder.local"
-    tls:
-      enabled: false
-      secretName: "gohoarder-frontend-tls"
-
-  # Ingress for API (if you want separate ingress)
-  api:
+  # Single ingress routes all traffic to frontend
+  # Frontend now includes reverse proxy to backend (merged gateway functionality)
+  host: "gohoarder.local"
+  tls:
     enabled: false
-    host: "api.gohoarder.local"
-    tls:
-      enabled: false
-      secretName: "gohoarder-api-tls"
+    secretName: "gohoarder-tls"
 
 # Autoscaling configuration
 autoscaling: