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>

app/assets/helpers.py

@@ -4,11 +4,27 @@ from decimal import Decimal
 from aiohttp import web
 from datetime import datetime, timezone
 from pathlib import Path
-from typing import Literal, Any
+from typing import Literal, Any, Sequence
 
 import folder_paths
 
 
+def pick_best_live_path(states: Sequence) -> str:
+    """
+    Return the best on-disk path among cache states:
+      1) Prefer a path that exists with needs_verify == False (already verified).
+      2) Otherwise, pick the first path that exists.
+      3) Otherwise return empty string.
+    """
+    alive = [s for s in states if getattr(s, "file_path", None) and os.path.isfile(s.file_path)]
+    if not alive:
+        return ""
+    for s in alive:
+        if not getattr(s, "needs_verify", False):
+            return s.file_path
+    return alive[0].file_path
+
+
 RootType = Literal["models", "input", "output"]
 ALLOWED_ROOTS: tuple[RootType, ...] = ("models", "input", "output")