feat(frontend): sprint 5 — templates CRUD pages + nav + picker modal + dropdown

- types.ts: SimulationTemplate, SimulationTemplateCreateInput, SimulationTemplatePatchInput,
  extend SimulationCreateInput with template_id
- api/templates.ts: listTemplates, getTemplate, createTemplate, updateTemplate, deleteTemplate
- hooks/useTemplates.ts: useTemplates, useTemplate, useCreateTemplate, useUpdateTemplate,
  useDeleteTemplate (TanStack Query, invalidates ["templates"])
- TemplatesListPage: /admin/templates — table (name, MITRE count, created by, updated),
  New/Edit/Delete actions, loading/error/empty states
- TemplateFormPage: /admin/templates/new + /admin/templates/:id/edit — controlled form
  with inline MITRE field (picker + matrix modal), ConfirmDialog for delete
- TemplatePickerModal: reusable modal listing templates with empty state (AC-27.6)
- SimulationList: replace "New simulation" link with split-button dropdown
  (Blank → /simulations/new | From template… → TemplatePickerModal + POST template_id)
- Layout: "Templates" nav link (admin | redteam, before "Users")
- App.tsx: /admin/templates routes gated roles=["admin","redteam"]
- 26 new Vitest tests (118 total, 92 original preserved)

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

frontend/src/App.tsx

@@ -8,6 +8,8 @@ import { EngagementFormPage } from '@/pages/EngagementFormPage';
 import { EngagementDetailPage } from '@/pages/EngagementDetailPage';
 import { UsersAdminPage } from '@/pages/UsersAdminPage';
 import { SimulationFormPage } from '@/pages/SimulationFormPage';
+import { TemplatesListPage } from '@/pages/TemplatesListPage';
+import { TemplateFormPage } from '@/pages/TemplateFormPage';
 
 /**
  * Router. Auth + role gates handled by <ProtectedRoute />.
@@ -43,6 +45,13 @@ export function App(): JSX.Element {
             <Route element={<ProtectedRoute roles={['admin']} />}>
               <Route path="/admin/users" element={<UsersAdminPage />} />
             </Route>
+
+            {/* admin + redteam routes */}
+            <Route element={<ProtectedRoute roles={['admin', 'redteam']} />}>
+              <Route path="/admin/templates" element={<TemplatesListPage />} />
+              <Route path="/admin/templates/new" element={<TemplateFormPage />} />
+              <Route path="/admin/templates/:id/edit" element={<TemplateFormPage />} />
+            </Route>
           </Route>
         </Route>