feat(example-images): add check pending models endpoint and improve async handling

- Add /api/example-images/check-pending endpoint to quickly check models needing downloads
- Improve DownloadManager.start_download() to return immediately without blocking
- Add _handle_download_task_done callback for proper error handling and progress saving
- Add check_pending_models() method for lightweight pre-download validation
- Update frontend ExampleImagesManager to use new check-pending endpoint
- Add comprehensive tests for new functionality

py/routes/example_images_route_registrar.py

@@ -30,6 +30,7 @@ ROUTE_DEFINITIONS: tuple[RouteDefinition, ...] = (
     RouteDefinition("POST", "/api/lm/force-download-example-images", "force_download_example_images"),
     RouteDefinition("POST", "/api/lm/cleanup-example-image-folders", "cleanup_example_image_folders"),
     RouteDefinition("POST", "/api/lm/example-images/set-nsfw-level", "set_example_image_nsfw_level"),
+    RouteDefinition("POST", "/api/lm/check-example-images-needed", "check_example_images_needed"),
 )
 
 

py/routes/handlers/example_images_handlers.py

@@ -92,6 +92,19 @@ class ExampleImagesDownloadHandler:
         except ExampleImagesDownloadError as exc:
             return web.json_response({'success': False, 'error': str(exc)}, status=500)
 
+    async def check_example_images_needed(self, request: web.Request) -> web.StreamResponse:
+        """Lightweight check to see if any models need example images downloaded."""
+        try:
+            payload = await request.json()
+            model_types = payload.get('model_types', ['lora', 'checkpoint', 'embedding'])
+            result = await self._download_manager.check_pending_models(model_types)
+            return web.json_response(result)
+        except Exception as exc:
+            return web.json_response(
+                {'success': False, 'error': str(exc)},
+                status=500
+            )
+
 
 class ExampleImagesManagementHandler:
     """HTTP adapters for import/delete endpoints."""
@@ -161,6 +174,7 @@ class ExampleImagesHandlerSet:
             "resume_example_images": self.download.resume_example_images,
             "stop_example_images": self.download.stop_example_images,
             "force_download_example_images": self.download.force_download_example_images,
+            "check_example_images_needed": self.download.check_example_images_needed,
             "import_example_images": self.management.import_example_images,
             "delete_example_image": self.management.delete_example_image,
             "set_example_image_nsfw_level": self.management.set_example_image_nsfw_level,