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/services/conftest.py

@@ -0,0 +1,49 @@
+import os
+import tempfile
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import Session
+
+from app.assets.database.models import Base
+
+
+@pytest.fixture
+def db_engine():
+    """In-memory SQLite engine for fast unit tests."""
+    engine = create_engine("sqlite:///:memory:")
+    Base.metadata.create_all(engine)
+    return engine
+
+
+@pytest.fixture
+def session(db_engine):
+    """Session fixture for tests that need direct DB access."""
+    with Session(db_engine) as sess:
+        yield sess
+
+
+@pytest.fixture
+def mock_create_session(db_engine):
+    """Patch create_session to use our in-memory database."""
+    from contextlib import contextmanager
+    from sqlalchemy.orm import Session as SASession
+
+    @contextmanager
+    def _create_session():
+        with SASession(db_engine) as sess:
+            yield sess
+
+    with patch("app.assets.services.ingest.create_session", _create_session), \
+         patch("app.assets.services.asset_management.create_session", _create_session), \
+         patch("app.assets.services.tagging.create_session", _create_session):
+        yield _create_session
+
+
+@pytest.fixture
+def temp_dir():
+    """Temporary directory for file operations."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        yield Path(tmpdir)