chore: migrate frontend assets to OSS and same-origin APIs

.env.example

@@ -1,8 +1,5 @@
-# Dev proxy target — the backend API server
-VITE_DEV_PROXY=http://47.110.225.76:3600
-
-# Key server URL for auth/profile endpoints
-VITE_KEY_SERVER_URL=
-
-# Main API base URL (used when not served from omniai.net.cn)
-VITE_API_BASE_URL=
+# Frontend environment variables are intentionally unsupported.
+#
+# API traffic must go through same-origin /api.
+# Public runtime settings must come from application APIs.
+# Provider keys and OSS credentials must stay on the server.