Fix: move theme+css to gr.Blocks(), not launch()

Gradio 6 on HF Spaces does not accept theme/css on launch().
Pass them at Blocks construction time instead.

app.py

@@ -593,7 +593,7 @@ _CARD_POST      = '<span class="tg-lbl">Post-processing</span>'
 
 # ---- UI -------------------------------------------------------------------
 
-with gr.Blocks(title="ThreeGen") as demo:
+with gr.Blocks(title="ThreeGen", theme=_build_theme(), css=_CSS) as demo:
 
     # Header
     gr.HTML(_HEADER_HTML, elem_id="tg-header")
@@ -686,4 +686,4 @@ with gr.Blocks(title="ThreeGen") as demo:
 
 
 if __name__ == "__main__":
-    demo.launch(theme=_build_theme(), css=_CSS)
+    demo.launch()