Refactor admin API into service and repository layers.

fix: 5 critical storage bugs + 3 SQLite/SSE bugs -- tracker.py: db.flush() after add() so chat messages/analytics are persisted -- chat.py: flush->commit for durable ChatSession row -- settings.py: fix session mismatch in all PUT routes (widget-config, profile, personality, notifications, password) - setattr on cross-session user was discarded; now uses UPDATE stmt on route db -- aggregator.py: replace PostgreSQL-only gen_random_uuid() with uuid4() param for SQLite -- ingest.py: fix SSE channel name mismatch subscriber vs publisher -- superadmin_service.py: fix naive/aware datetime TypeError in extend_subscription

refactor: Phase 6A+6B — top-level imports and Pydantic schema upgrades

Refactor: 10/10 modularity — pipeline/ package, admin/routers/ split, guards single source of truth