Fix HunyuanFoley xregen AttributeError: return torch.device from _get_device_and_dtype

denoise_process calls torch.autocast(device_type=device.type, ...) which
requires a torch.device object. _get_device_and_dtype was returning a plain
string 'cuda', causing AttributeError: 'str' object has no attribute 'type'.
All other usages (.to(), map_location=, device=) work with torch.device too.

app.py

@@ -175,8 +175,9 @@ def _ensure_syspath(subdir: str) -> str:
 
 
 def _get_device_and_dtype() -> tuple:
-    """Return (device, weight_dtype) pair used by all GPU functions."""
-    device = "cuda" if torch.cuda.is_available() else "cpu"
+    """Return (device, weight_dtype) pair used by all GPU functions.
+    Returns a torch.device object so callers can use device.type safely."""
+    device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
     return device, torch.bfloat16