feat: wire model-downloader routes and feature flags into the server

Registers the model-downloader routes during PromptServer startup and
advertises the capability via comfy_api feature flags so the frontend
can detect server-side download support.

comfy_api/feature_flags.py

@@ -98,12 +98,24 @@ def _parse_cli_feature_flags() -> dict[str, Any]:
 
 
 # Default server capabilities
+def _hf_auth_eligible_at_startup() -> bool:
+    """Snapshot eligibility once at feature-flag init time.
+
+    Imports lazily because the flags module loads very early in the
+    server boot sequence — earlier than the model_downloader package.
+    """
+    from app.model_downloader.hf_auth.eligibility import is_hf_auth_eligible
+    return is_hf_auth_eligible()
+
+
 _CORE_FEATURE_FLAGS: dict[str, Any] = {
     "supports_preview_metadata": True,
     "max_upload_size": args.max_upload_size * 1024 * 1024, # Convert MB to bytes
     "extension": {"manager": {"supports_v4": True}},
     "node_replacements": True,
     "assets": args.enable_assets,
+    "server_side_model_downloads": True,
+    "hf_auth_eligible": _hf_auth_eligible_at_startup(),
 }
 
 # CLI-provided flags cannot overwrite core flags

server.py

@@ -47,6 +47,7 @@ from app.assets.seeder import asset_seeder
 from app.assets.api.routes import register_assets_routes
 from app.assets.services.ingest import register_file_in_place
 from app.assets.services.asset_management import resolve_hash_to_path
+from app.model_downloader.api.routes import register_routes as register_model_downloader_routes
 
 from app.user_manager import UserManager
 from app.model_manager import ModelFileManager
@@ -256,6 +257,7 @@ class PromptServer():
         else:
             register_assets_routes(self.app)
             asset_seeder.disable()
+        register_model_downloader_routes(self.app)
         routes = web.RouteTableDef()
         self.routes = routes
         self.last_node_id = None