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/package.json

@@ -13,6 +13,9 @@
     "format:check": "prettier --check \"src/**/*.{ts,tsx,css,json,html}\""
   },
   "dependencies": {
+    "@dnd-kit/core": "^6.1.0",
+    "@dnd-kit/sortable": "^8.0.0",
+    "@dnd-kit/utilities": "^3.2.2",
     "@fontsource/ibm-plex-sans": "^5.0.20",
     "@fontsource/jetbrains-mono": "^5.0.20",
     "@tanstack/react-query": "^5.51.0",