feat: video loader + combiner nodes

Adapted from HunyuanVideo-FoleyTune for the audio-SR workflow:

- UniverSR Load Video Audio: extract a video's audio track via ffmpeg
  (WAV pipe + soundfile, no torchcodec) and carry a UNIVERSR_VIDEO
  reference forward, with an inline video preview.
- UniverSR Video Combiner: mux the enhanced audio back onto the source
  video without re-encoding video (-c:v copy), trim-aware, with output
  auto-increment and preview.

Both registered alongside the SR nodes; ffmpeg + soundfile required only
for these. Adds README docs and an example video workflow.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

__init__.py

@@ -1,10 +1,20 @@
 """ComfyUI-UniverSR — vocoder-free audio super-resolution (8/12/16/24 kHz -> 48 kHz)."""
 
+NODE_CLASS_MAPPINGS = {}
+NODE_DISPLAY_NAME_MAPPINGS = {}
+
 try:
-    from .nodes import NODE_CLASS_MAPPINGS, NODE_DISPLAY_NAME_MAPPINGS
-except Exception as e:  # surface import errors in the ComfyUI log without crashing startup
-    print(f"[ComfyUI-UniverSR] Failed to load nodes: {e}")
-    NODE_CLASS_MAPPINGS = {}
-    NODE_DISPLAY_NAME_MAPPINGS = {}
+    from .nodes import NODE_CLASS_MAPPINGS as _sr_nodes, NODE_DISPLAY_NAME_MAPPINGS as _sr_display
+    NODE_CLASS_MAPPINGS.update(_sr_nodes)
+    NODE_DISPLAY_NAME_MAPPINGS.update(_sr_display)
+except Exception as e:  # surface errors in the ComfyUI log without crashing startup
+    print(f"[ComfyUI-UniverSR] Failed to load SR nodes: {e}")
+
+try:
+    from .nodes_video import NODE_CLASS_MAPPINGS as _vid_nodes, NODE_DISPLAY_NAME_MAPPINGS as _vid_display
+    NODE_CLASS_MAPPINGS.update(_vid_nodes)
+    NODE_DISPLAY_NAME_MAPPINGS.update(_vid_display)
+except Exception as e:  # video nodes are optional (need ffmpeg/soundfile)
+    print(f"[ComfyUI-UniverSR] Failed to load video nodes: {e}")
 
 __all__ = ["NODE_CLASS_MAPPINGS", "NODE_DISPLAY_NAME_MAPPINGS"]