Why:
- Dashboard needs system health, Qdrant management, chunk preview, questions, and cost estimation endpoints
Changes:
- Add admin router with 11 endpoints (health, Qdrant CRUD, chunk preview, questions management, cost estimation)
- Add delete_experiment to SQLite storage
- Mount admin router and dashboard static files at /app
Impact:
- New /admin/* API routes available
- Dashboard served at /app/ via StaticFiles