Refactor asset database: separate business logic from queries

Architecture changes:
- API Routes -> manager.py (thin adapter) -> services/ (business logic) -> queries/ (atomic DB ops)
- Services own session lifecycle via create_session()
- Queries accept Session as parameter, do single-table atomic operations

New app/assets/services/ layer:
- __init__.py - exports all service functions
- ingest.py - ingest_file_from_path(), register_existing_asset()
- asset_management.py - get_asset_detail(), update_asset_metadata(), delete_asset_reference(), set_asset_preview()
- tagging.py - apply_tags(), remove_tags(), list_tags()

Removed from queries/asset_info.py:
- ingest_fs_asset (moved to services/ingest.py as ingest_file_from_path)
- update_asset_info_full (moved to services/asset_management.py as update_asset_metadata)
- create_asset_info_for_existing_asset (moved to services/ingest.py as register_existing_asset)

Updated manager.py:
- Now a thin adapter that transforms API schemas to/from service calls
- Delegates all business logic to services layer
- No longer imports sqlalchemy.orm.Session or models directly

Test updates:
- Fixed test_cache_state.py import of pick_best_live_path (moved to helpers.py)
- Added comprehensive service layer tests (41 new tests)
- All 112 query + service tests pass

Amp-Thread-ID: https://ampcode.com/threads/T-019c24e2-7ae4-707f-ad19-c775ed8b82b5
Co-authored-by: Amp <amp@ampcode.com>

tests-unit/assets_test/queries/test_cache_state.py

@@ -2,10 +2,8 @@
 from sqlalchemy.orm import Session
 
 from app.assets.database.models import Asset, AssetCacheState
-from app.assets.database.queries import (
-    list_cache_states_by_asset_id,
-    pick_best_live_path,
-)
+from app.assets.database.queries import list_cache_states_by_asset_id
+from app.assets.helpers import pick_best_live_path
 
 
 def _make_asset(session: Session, hash_val: str | None = None, size: int = 1024) -> Asset: