feat(dashboard): GuruConnect v2 Support Codes view

Generate, list, and cancel attended-support codes (XXX-XXX-XXX), built
on the v2 codes API and existing UI primitives.

- Codes table: code in mono, status badge (pending+pulse/connected/
  completed/cancelled), bound client/machine, created-by, created
  (relative + absolute tooltip). Sticky header, skeleton load,
  actionable empty/error states.
- Generate opens a focused reveal modal showing the code large in
  JetBrains Mono with copy and a read-aloud instruction; the code is
  announced character-by-character for screen readers. Mint is ref-
  guarded so it creates exactly one code per open (no StrictMode dupe).
- Cancel via confirm dialog (POST /api/codes/:code/cancel), disabled for
  non-cancellable statuses; invalidates the codes query. List polls 7s.
- Shared API client now tolerates non-JSON 200 bodies, so the cancel
  endpoint's plain-text "Code cancelled" success no longer surfaces as a
  failure. Error-envelope handling unchanged.

Passed Code Review (no blockers after fixes) and local gates
(tsc/lint/build green).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

dashboard/src/features/codes/hooks.ts

@@ -0,0 +1,55 @@
+import {
+  useMutation,
+  useQuery,
+  useQueryClient,
+} from "@tanstack/react-query";
+import * as codesApi from "../../api/codes";
+import type { CreateCodeRequest } from "../../api/types";
+
+const CODES_KEY = ["codes"] as const;
+
+/**
+ * List the active support codes. Polls on a short interval because codes are
+ * short-lived: a `pending` code can be redeemed (-> `connected`) or expire out
+ * of the active set at any moment, and a tech who just read a code aloud is
+ * watching for exactly that transition. The interval is tight (like the
+ * sessions poll) so the redeem shows up on its own without a manual refresh.
+ */
+export function useSupportCodes() {
+  return useQuery({
+    queryKey: CODES_KEY,
+    queryFn: ({ signal }) => codesApi.listCodes(signal),
+    refetchInterval: 7_000,
+    staleTime: 3_500,
+  });
+}
+
+/**
+ * Generate a new support code, then invalidate the list so the new `pending`
+ * code appears in the table. The created code is returned to the caller so the
+ * generate flow can surface it prominently (it is read to the end user).
+ */
+export function useGenerateCode() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (body: CreateCodeRequest) => codesApi.createCode(body),
+    onSuccess: () => {
+      void qc.invalidateQueries({ queryKey: CODES_KEY });
+    },
+  });
+}
+
+/**
+ * Cancel (revoke) a support code, then invalidate the list so the row drops out
+ * of the active set. Cancelling an un-redeemed code is irreversible, so the UI
+ * confirms first; this hook is the action behind that confirmation.
+ */
+export function useCancelCode() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (code: string) => codesApi.cancelCode(code),
+    onSuccess: () => {
+      void qc.invalidateQueries({ queryKey: CODES_KEY });
+    },
+  });
+}