Fix Gradio 6 deprecation warning: move theme/css out of Blocks constructor

In Gradio 6, `theme` and `css` parameters were removed from the
`gr.Blocks()` constructor and must only be passed to `launch()`.
Passing them in both places caused a UserWarning on every import.

app.py

@@ -121,7 +121,7 @@ def inspect_state(seed):
 # Gradio UI
 # -------------------------------------------------------------------
 
-with gr.Blocks(title="SentinelOps Arena", fill_width=True, theme=SentinelTheme(), css=CUSTOM_CSS) as demo:
+with gr.Blocks(title="SentinelOps Arena", fill_width=True) as demo:
 
     # Header banner
     gr.HTML(HEADER_HTML)