refactor: move scanner to services layer with pure query extraction

- Move app/assets/scanner.py to app/assets/services/scanner.py
- Extract pure queries from fast_db_consistency_pass:
  - get_cache_states_for_prefixes()
  - bulk_set_needs_verify()
  - delete_cache_states_by_ids()
  - delete_orphaned_seed_asset()
- Split prune_orphaned_assets into pure queries:
  - delete_cache_states_outside_prefixes()
  - get_orphaned_seed_asset_ids()
  - delete_assets_by_ids()
- Add reconcile_cache_states_for_root() service function
- Add prune_orphaned_assets() service function
- Remove function injection pattern
- Update imports in main.py, server.py, routes.py

Amp-Thread-ID: https://ampcode.com/threads/T-019c24f1-3385-701b-87e0-8b6bc87e841b
Co-authored-by: Amp <amp@ampcode.com>

main.py

@@ -7,7 +7,7 @@ import folder_paths
 import time
 from comfy.cli_args import args, enables_dynamic_vram
 from app.logger import setup_logger
-from app.assets.scanner import seed_assets
+from app.assets.services.scanner import seed_assets
 import itertools
 import utils.extra_config
 import logging