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/App.tsx

@@ -5,6 +5,7 @@ import { ProtectedRoute } from "./auth/ProtectedRoute";
 import { AppShell } from "./components/layout/AppShell";
 import { ToastProvider } from "./components/ui/toast";
 import { LoginPage } from "./features/auth/LoginPage";
+import { SupportCodesPage } from "./features/codes/SupportCodesPage";
 import { MachinesPage } from "./features/machines/MachinesPage";
 import { SessionsPage } from "./features/sessions/SessionsPage";
 
@@ -29,7 +30,8 @@ export function App() {
                 <Route element={<AppShell />}>
                   <Route path="/machines" element={<MachinesPage />} />
                   <Route path="/sessions" element={<SessionsPage />} />
-                  {/* Codes / Users land in later passes. */}
+                  <Route path="/codes" element={<SupportCodesPage />} />
+                  {/* Users lands in a later pass. */}
                   <Route path="/" element={<Navigate to="/machines" replace />} />
                 </Route>
               </Route>