fix: disable enhance_prompt by default to prevent dark/garbage output

Gemma prompt enhancement causes token overflow (1087 > 1024) which
corrupts the prompt to garbage like '/imagine synchronized lipsync.'
This produces dark/nonsensical video output.

Disable by default; users can still enable it manually in Advanced Settings.

app.py

@@ -924,7 +924,7 @@ def generate_video(
     prompt: str = "",
     duration: float = 3,
     conditioning_strength: float = 0.85, 
-    enhance_prompt: bool = True,
+    enhance_prompt: bool = False,
     use_video_audio: bool = True,
     seed: int = 42,
     randomize_seed: bool = True,
@@ -1198,7 +1198,7 @@ with gr.Blocks(title="LTX 2.3 Sync", css=css, theme=purple_citrus) as demo:
             )
 
             with gr.Accordion("Advanced Settings", open=False):
-                enhance_prompt = gr.Checkbox(label="Enhance Prompt", value=True)
+                enhance_prompt = gr.Checkbox(label="Enhance Prompt", value=False)
                 conditioning_strength = gr.Slider(
                     label="V2V Conditioning Strength",
                     info="How closely to follow the reference video's structure",