feat(m5): admin SPA pages for the template catalogue

- AdminTestsPage with filters (q, tactic, opsec, tag), modal-based CRUD,
  markdown textareas for procedure/result/detection, embedded MitreTagPicker
  for tagging.
- AdminScenariosPage with @dnd-kit/sortable drag-and-drop on the ordered
  test list, two-step save (PATCH metadata + PUT tests), catalogue picker
  excluding soft-deleted items.
- lib/templates.ts typed client + queryKey factory.
- MarkdownField helper (textarea with markdown hint label).
- Layout adds Tests + Scenarios admin nav links; App.tsx routes both
  behind RequireAdmin.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -6,6 +6,8 @@ import { RequireAdmin } from '@/components/RequireAdmin';
 import { RequireAuth } from '@/components/RequireAuth';
 import { AdminGroupsPage } from '@/pages/AdminGroupsPage';
 import { AdminInvitationsPage } from '@/pages/AdminInvitationsPage';
+import { AdminScenariosPage } from '@/pages/AdminScenariosPage';
+import { AdminTestsPage } from '@/pages/AdminTestsPage';
 import { AdminUsersPage } from '@/pages/AdminUsersPage';
 import { HomePage } from '@/pages/HomePage';
 import { MitrePage } from '@/pages/MitrePage';
@@ -82,6 +84,22 @@ function App() {
                   </RequireAdmin>
                 }
               />
+              <Route
+                path="/admin/tests"
+                element={
+                  <RequireAdmin>
+                    <AdminTestsPage />
+                  </RequireAdmin>
+                }
+              />
+              <Route
+                path="/admin/scenarios"
+                element={
+                  <RequireAdmin>
+                    <AdminScenariosPage />
+                  </RequireAdmin>
+                }
+              />
               <Route path="*" element={<Navigate to="/" replace />} />
             </Route>
           </Routes>