refactor: redesign admin permalinks to RESTful paths

- Replace fragile /admin/ai-playground and /admin/ai-generation routes
  with item-scoped /admin/questions/{id}/generate endpoints
- Add /admin/tryouts/{id}/questions route using Tryout primary key
  instead of composite query params (?tryout_id=X&website_id=Y)
- Fix variant detail and review-bulk endpoints to use scoped paths
- Update all internal links (dashboard, hierarchy, exams) to new routes
- Remove obsolete ai_playground_view/submit/save functions

test_fetch.py

@@ -0,0 +1,9 @@
+import asyncio
+from fastapi.testclient import TestClient
+from app.main import app
+
+client = TestClient(app)
+client.post("/admin/login", data={"username": "admin", "password": "password"})
+response = client.get("/admin/hierarchy")
+print(response.status_code)
+print(response.text)