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/api/client.ts

@@ -117,7 +117,14 @@ async function request<T>(path: string, opts: RequestOptions = {}): Promise<T> {
   if (res.status === 204) return undefined as T;
   const text = await res.text();
   if (!text) return undefined as T;
-  return JSON.parse(text) as T;
+  // Most success responses are JSON, but some routes return a plain-text body
+  // on 200 (e.g. cancel returns "Code cancelled"). Tolerate non-JSON so a
+  // successful call isn't surfaced as a SyntaxError failure.
+  try {
+    return JSON.parse(text) as T;
+  } catch {
+    return undefined as T;
+  }
 }
 
 export const http = {