feat(api): expose registered extension filters on /experiment/models (#14797)

Each folder in the listing now carries its registered extension
allowlist verbatim; an empty array means the folder accepts any
extension (match-all), mirroring filter_files_extensions semantics.

Gives consumers the filtering rule itself rather than just its output:
/models/{folder} lists files by the per-folder rule but the rule is not
exposed anywhere, and /experiment/models/{folder} filters everything by
the global supported_pt_extensions regardless of registration.
Presentation-level filtering of match-all folders (e.g. hiding
README/config noise that repository-downloading custom nodes leave in
model directories) is deliberately left to the consumer.

Co-authored-by: guill <jacob.e.segal@gmail.com>

app/model_manager.py

@@ -35,7 +35,11 @@ class ModelFileManager:
             for folder in model_types:
                 if folder in folder_black_list:
                     continue
-                output_folders.append({"name": folder, "folders": folder_paths.get_folder_paths(folder)})
+                output_folders.append({
+                    "name": folder,
+                    "folders": folder_paths.get_folder_paths(folder),
+                    "extensions": sorted(folder_paths.folder_names_and_paths[folder][1]),
+                })
             return web.json_response(output_folders)
 
         # NOTE: This is an experiment to replace `/models/{folder}`