feat(frontend): c2 config card + execute modal (sprint 8 phase 1)

- frontend/src/api/c2.ts: 6 typed API calls (getC2Config, putC2Config,
  deleteC2Config, testC2Config, listCallbacks, executeC2) following the
  frozen M1+M2 backend contracts
- frontend/src/api/types.ts: C2Config, C2ConfigInput, C2TestResult,
  C2Callback, C2CallbacksResponse, C2Task, C2ExecuteInput, C2ExecuteResponse
- frontend/src/hooks/useC2.ts: useC2Config, useUpdateC2Config,
  useDeleteC2Config, useTestC2Config, useC2Callbacks, useExecuteC2
- frontend/src/components/C2ConfigCard.tsx: engagement-scoped C2 config
  card (url + write-only token + verify-tls + save/delete/test-connection),
  503 disabled state, ConfirmDialog on delete
- frontend/src/components/ExecuteViaC2Modal.tsx: callback picker table
  (mono data cells), commands textarea pre-filled from rt.commands,
  Launch disabled until row selected + non-empty commands
- frontend/src/pages/EngagementFormPage.tsx: embed C2ConfigCard in edit
  mode only, admin+redteam only (canEditEngagements gate)
- frontend/src/pages/SimulationFormPage.tsx: Execute via C2 button in RT
  card, visible only when !isDone && canEditRT && hasC2Config; opens modal
- Tests: 33 new tests across api/c2, components/C2ConfigCard,
  components/ExecuteViaC2Modal, EngagementFormPage, SimulationFormPage
  (172 total, 139 baseline + 33 new, all passing)

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

frontend/src/pages/EngagementFormPage.tsx

@@ -7,10 +7,12 @@ import {
   useEngagement,
   usePatchEngagement,
 } from '@/hooks/useEngagements';
+import { useAuth } from '@/hooks/useAuth';
 import { useToast } from '@/hooks/useToast';
 import { FormField, Select, TextArea, TextInput } from '@/components/FormField';
 import { LoadingState } from '@/components/LoadingState';
 import { ErrorState } from '@/components/ErrorState';
+import { C2ConfigCard } from '@/components/C2ConfigCard';
 
 const STATUS_OPTIONS: { value: EngagementStatus; label: string }[] = [
   { value: 'planned', label: 'Planned' },
@@ -50,6 +52,7 @@ export function EngagementFormPage(): JSX.Element {
   const numericId = id ? Number(id) : undefined;
   const navigate = useNavigate();
   const { push } = useToast();
+  const { canEditEngagements } = useAuth();
 
   const detail = useEngagement(editing ? numericId : undefined);
   const createMutation = useCreateEngagement();
@@ -214,6 +217,10 @@ export function EngagementFormPage(): JSX.Element {
           </Link>
         </div>
       </form>
+
+      {editing && numericId && canEditEngagements && (
+        <C2ConfigCard engagementId={numericId} />
+      )}
     </div>
   );
 }