fix(backend): validate configured model provider pair

backend/src/routes/settings.ts

@@ -25,15 +25,19 @@ export function settingsRoutes(
   app.put("/settings", async (req, reply) => {
     const b = (req.body ?? {}) as Settings;
     if (b.model) {
-      let available: { id: string }[] = [];
+      let available: { provider: string; id: string }[] = [];
       try {
         available = await deps.listModels();
       } catch {
         available = [];
       }
       // Only validate when Pi gave us a non-empty list; otherwise allow (degraded).
-      if (available.length > 0 && !available.some((m) => m.id === b.model)) {
-        return reply.code(400).send({ error: `Unknown model: ${b.model}` });
+      if (available.length > 0 && !available.some(
+        (candidate) => candidate.provider === b.provider && candidate.id === b.model,
+      )) {
+        return reply.code(400).send({
+          error: `Unknown model: ${b.provider ?? "unknown"}/${b.model}`,
+        });
       }
     }
     const next: Settings = {