feat: implement full admin panel with dashboard, user management, and platform settings

Adds complete super_admin panel with 9 pages and account owner categories page.
Backend includes 5 new DB tables, ~25 API endpoints, settings manager with
in-memory cache, and 29 integration tests. Frontend includes reusable admin
components (DataTable, Pagination, ActionMenu, etc.) with code-split lazy loading.

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

frontend/package.json

@@ -15,11 +15,13 @@
     "@dnd-kit/sortable": "^10.0.0",
     "@dnd-kit/utilities": "^3.2.2",
     "@stripe/stripe-js": "^8.7.0",
+    "@types/lodash": "^4.17.23",
     "axios": "^1.13.4",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "date-fns": "^4.1.0",
     "immer": "^11.1.3",
+    "lodash": "^4.17.23",
     "lucide-react": "^0.563.0",
     "react": "^19.2.0",
     "react-day-picker": "^9.13.1",