Update app.py to enable GPU support and streamline model download process

Modify the run_training function to utilize GPU support with the @spaces.GPU decorator. Additionally, ensure the _startup_download_models function is called during the application startup, enhancing the model loading process. These changes improve performance and user experience by leveraging GPU capabilities and ensuring necessary models are downloaded at launch.

app.py

@@ -12,7 +12,7 @@ import json
 
 import gradio as gr
 import importlib
-# import spaces
+import spaces
 
 # Local modules
 from download_qwen_image_models import download_all_models, DEFAULT_MODELS_DIR
@@ -837,7 +837,7 @@ def _startup_install_musubi_deps() -> None:
             print("[QIE] WARN: musubi-tuner installation failed. Continuing.")
 
 
-# @spaces.GPU
+@spaces.GPU
 def run_training(
     output_name: str,
     caption: str,
@@ -2008,7 +2008,7 @@ if __name__ == "__main__":
     _startup_install_musubi_deps()
 
     # 2) Download models at startup (blocking by design)
-    # _startup_download_models()
+    _startup_download_models()
 
     # 3) Launch Gradio app
     ui = build_ui()