fix: bug sweep and improvements

- nodes/__init__.py: fix [PrismAudio] leftover label in error print
- selva_feature_extractor: hash beginning, middle and end of video tensor
  instead of just first 1MB, avoiding collisions on videos with same opening frames
- selva_sampler: derive SequenceConfig from model template via dataclasses.replace
  instead of hardcoding sampling_rate/spectrogram_frame_rate per mode

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nodes/__init__.py

@@ -14,4 +14,4 @@ for key, (module_path, class_name, display_name) in _NODES.items():
         NODE_CLASS_MAPPINGS[key] = getattr(mod, class_name)
         NODE_DISPLAY_NAME_MAPPINGS[key] = display_name
     except (ImportError, AttributeError) as e:
-        print(f"[PrismAudio] Skipping {key}: {e}")
+        print(f"[SelVA] Skipping {key}: {e}")