Extract single shared Database pool, eliminate 4 duplicated pool creations ...

- Create navi/db.py::Database managing one asyncpg pool
- KvStore, PgSessionStore, MemoryStore, RecallScheduler now accept pool in constructor
- AppContainer holds Database, shutdown closes one pool instead of 4
- create_container creates one pool and passes it to all stores
- All tests updated to set _initialized=True on fakes to skip DDL

392 passed, 1 skipped

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Extract WebSocket business logic into AgentSessionOrchestrator ...

- Create navi/core/orchestrator.py with AgentSessionOrchestrator and SessionRun
- Orchestrator owns _runs, _busy_sessions, Agent creation, run_agent(), run_recall()
- Transport-agnostic: accepts notify callback from WebSocket handler
- WebSocket handler (websocket.py) now only does serialization/deserialization
- _fire_recall delegates to orchestrator.run_recall() instead of inline logic
- recall_scheduler_loop now accepts orchestrator parameter
- AppContainer gains .orchestrator field, created in create_container()
- deps.py: add get_orchestrator()
- Update integration tests for scheduler_loop and websocket unit tests

All 392 tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Fix PgSessionStore import in container.py ...

`PgSessionStore` lives in `navi.core.pg_session_store`, not `navi.core.session`.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Replace global lazy singletons with explicit AppContainer + lifespan ...

- Create navi/core/container.py with AppContainer dataclass and create_container()
- Rewrite navi/api/deps.py: remove module-level singletons, add _container global
  fallback + set_container(), use _resolve_container() for all getters
- Replace @app.on_event with @asynccontextmanager lifespan in main.py
- Update routes to use Depends(get_scheduler) instead of calling get_scheduler()
- Fix FastAPI body parsing bug: remove dataclass parameters from Depends getters
  (FastAPI was treating AppContainer sub-dependencies as Body params, forcing
  embed=True on all endpoint body params and causing 422 errors)
- Update websocket.py to use _resolve_container() instead of get_registries()
- Update integration test fixtures to build AppContainer and call set_container()
- Remove obsolete tests/unit/test_startup.py (tests removed _on_startup)
- Fix test_scheduler_loop.py fixture (get_registries no longer exists)

All 387 tests pass (excluding websocket hang tests).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>