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/database/queries/asset.py

@@ -29,3 +29,46 @@ def get_asset_by_hash(
     return (
         session.execute(select(Asset).where(Asset.hash == asset_hash).limit(1))
     ).scalars().first()
+
+
+def upsert_asset(
+    session: Session,
+    *,
+    asset_hash: str,
+    size_bytes: int,
+    mime_type: str | None = None,
+) -> tuple[Asset, bool, bool]:
+    """Upsert an Asset by hash. Returns (asset, created, updated)."""
+    from sqlalchemy.dialects import sqlite
+    
+    vals = {"hash": asset_hash, "size_bytes": int(size_bytes)}
+    if mime_type:
+        vals["mime_type"] = mime_type
+
+    ins = (
+        sqlite.insert(Asset)
+        .values(**vals)
+        .on_conflict_do_nothing(index_elements=[Asset.hash])
+    )
+    res = session.execute(ins)
+    created = int(res.rowcount or 0) > 0
+
+    asset = session.execute(
+        select(Asset).where(Asset.hash == asset_hash).limit(1)
+    ).scalars().first()
+    if not asset:
+        raise RuntimeError("Asset row not found after upsert.")
+
+    updated = False
+    if not created:
+        changed = False
+        if asset.size_bytes != int(size_bytes) and int(size_bytes) > 0:
+            asset.size_bytes = int(size_bytes)
+            changed = True
+        if mime_type and asset.mime_type != mime_type:
+            asset.mime_type = mime_type
+            changed = True
+        if changed:
+            updated = True
+
+    return asset, created, updated