Fix ZeroGPU kwarg stripping: make silent_video/segments_json positional

ZeroGPU only forwards positional args to the GPU worker process — kwargs
are silently dropped, arriving as None and causing json.loads(None) crash.

Make silent_video, segments_json (MMAudio) and silent_video, segments_json,
total_dur_s (HunyuanFoley) required positional params in the gpu_infer
functions so ZeroGPU passes them through correctly.

app.py

@@ -1015,7 +1015,7 @@ def _mmaudio_duration(video_file, prompt, negative_prompt, seed_val,
 @spaces.GPU(duration=_mmaudio_duration)
 def _mmaudio_gpu_infer(video_file, prompt, negative_prompt, seed_val,
                        cfg_strength, num_steps, crossfade_s, crossfade_db, num_samples,
-                       silent_video=None, segments_json=None):
+                       silent_video, segments_json):
     """GPU-only MMAudio inference — model loading + flow-matching generation.
     Returns list of (seg_audios, sr) per sample.
 
@@ -1163,7 +1163,7 @@ def _hunyuan_duration(video_file, prompt, negative_prompt, seed_val,
 @spaces.GPU(duration=_hunyuan_duration)
 def _hunyuan_gpu_infer(video_file, prompt, negative_prompt, seed_val,
                        guidance_scale, num_steps, model_size, crossfade_s, crossfade_db,
-                       num_samples, silent_video=None, segments_json=None, total_dur_s=None):
+                       num_samples, silent_video, segments_json, total_dur_s):
     """GPU-only HunyuanFoley inference — model loading + feature extraction + denoising.
     Returns list of (seg_wavs, sr, text_feats) per sample.