Configure Vite dev proxy via VITE_BACKEND_URL

frontend/.env.example

@@ -0,0 +1,2 @@
+# Local frontend development without Docker
+VITE_BACKEND_URL=http://localhost:8000

frontend/vite.config.ts

@@ -30,7 +30,7 @@ export default defineConfig({
         // In the dev compose stack the backend is reachable via its service
         // name on the shared Docker/Podman network.  Using "localhost" would
         // resolve to the frontend container itself and cause ECONNREFUSED.
-        target: "http://backend:8000",
+        target: process.env["VITE_BACKEND_URL"] ?? "http://backend:8000",
         changeOrigin: true,
       },
     },