feat(feedback): add frontend feedback API client

Adds upsertFeedback and deleteFeedback API functions backed by
fetchWithAuth, targeting the /api/threads/{id}/runs/{id}/feedback
endpoint.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/core/api/feedback.ts

@@ -0,0 +1,42 @@
+import { getBackendBaseURL } from "../config";
+
+import { fetchWithAuth } from "./fetcher";
+
+export interface FeedbackData {
+  feedback_id: string;
+  rating: number;
+  comment: string | null;
+}
+
+export async function upsertFeedback(
+  threadId: string,
+  runId: string,
+  rating: number,
+  comment?: string,
+): Promise<FeedbackData> {
+  const res = await fetchWithAuth(
+    `${getBackendBaseURL()}/api/threads/${encodeURIComponent(threadId)}/runs/${encodeURIComponent(runId)}/feedback`,
+    {
+      method: "PUT",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ rating, comment: comment ?? null }),
+    },
+  );
+  if (!res.ok) {
+    throw new Error(`Failed to submit feedback: ${res.status}`);
+  }
+  return res.json();
+}
+
+export async function deleteFeedback(
+  threadId: string,
+  runId: string,
+): Promise<void> {
+  const res = await fetchWithAuth(
+    `${getBackendBaseURL()}/api/threads/${encodeURIComponent(threadId)}/runs/${encodeURIComponent(runId)}/feedback`,
+    { method: "DELETE" },
+  );
+  if (!res.ok && res.status !== 404) {
+    throw new Error(`Failed to delete feedback: ${res.status}`);
+  }
+}