fix(backend): validate configured model provider pair

backend/src/routes/meta.ts

@@ -34,7 +34,11 @@ export function metaRoutes(
     const fn = deps.listModels ?? (async () => []);
     try {
       return { models: await fn() };
-    } catch {
+    } catch (error) {
+      app.log.warn({
+        component: "pi-model-list",
+        errorType: error instanceof Error ? error.name : typeof error,
+      }, "Pi model listing failed");
       // Graceful fallback: Pi may not be running; don't crash the server.
       return { models: [] as PiModel[] };
     }