Configure Vite dev proxy via VITE_BACKEND_URL

Docs/Web-Development.md

@@ -135,9 +135,13 @@ frontend/
 ```
 
 > **Dev proxy target:** `vite.config.ts` proxies all `/api` requests to
-> `http://backend:8000`.  Use the compose **service name** (`backend`), not
-> `localhost` — inside the container network `localhost` resolves to the
-> frontend container itself and causes `ECONNREFUSED`.
+> `http://backend:8000` by default.  Set `VITE_BACKEND_URL` in `frontend/.env`
+> or your shell to override the backend address for local development outside
+> Docker.
+>
+> Use the compose **service name** (`backend`), not `localhost` — inside the
+> container network `localhost` resolves to the frontend container itself and
+> causes `ECONNREFUSED`.
 
 ### Separation of Concerns