Exclude hidden files and custom_nodes folder from asset scanning

- Filter hidden files/directories (dot-prefixed) in collect_models_files()
  using is_visible(), matching the existing behavior for input/output roots
- Exclude the 'custom_nodes' folder name from get_comfy_models_folders();
  custom nodes that register their own paths under other folder names
  will still be scanned as expected

Amp-Thread-ID: https://ampcode.com/threads/T-019c924b-591a-725e-b8b7-0d49ba1a5591
Co-authored-by: Amp <amp@ampcode.com>

app/assets/services/path_utils.py

@@ -7,14 +7,20 @@ from app.assets.database.queries import list_references_by_asset_id
 from app.assets.helpers import normalize_tags, select_best_live_path
 
 
+_NON_MODEL_FOLDER_NAMES = frozenset({"custom_nodes"})
+
+
 def get_comfy_models_folders() -> list[tuple[str, list[str]]]:
     """Build list of (folder_name, base_paths[]) for all model locations.
 
     Includes every category registered in folder_names_and_paths,
-    regardless of whether its paths are under the main models_dir.
+    regardless of whether its paths are under the main models_dir,
+    but excludes non-model entries like custom_nodes.
     """
     targets: list[tuple[str, list[str]]] = []
     for name, values in folder_paths.folder_names_and_paths.items():
+        if name in _NON_MODEL_FOLDER_NAMES:
+            continue
         paths, _exts = values[0], values[1]
         if paths:
             targets.append((name, paths))