feat: add data_utils package with FeaturesUtils implementation

Creates data_utils/v2a_utils/feature_utils_288.py with FeaturesUtils:
- T5-Gemma text encoding via transformers
- VideoPrism video encoding via JAX videoprism package
- Synchformer visual encoder loading from checkpoint

Also fixes extract_features.py to add plugin root to sys.path so
data_utils is importable in the subprocess venv.

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

scripts/extract_features.py

@@ -1,14 +1,10 @@
 #!/usr/bin/env python3
 """
 Standalone PrismAudio feature extraction script.
-Run in a separate conda env with JAX/TF installed.
+Runs in a separate Python env with JAX/TF installed (auto-created by PrismAudioFeatureExtractor).
 
 Usage:
     python extract_features.py --video input.mp4 --cot_text "description..." --output features.npz
-
-Setup:
-    conda env create -f environment.yml
-    conda activate prismaudio-extract
 """
 
 import argparse
@@ -17,6 +13,12 @@ import sys
 import numpy as np
 import torch
 
+# Add plugin root to sys.path so data_utils (and prismaudio_core) are importable
+_SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+_PLUGIN_DIR = os.path.dirname(_SCRIPT_DIR)
+if _PLUGIN_DIR not in sys.path:
+    sys.path.insert(0, _PLUGIN_DIR)
+
 
 def main():
     parser = argparse.ArgumentParser(description="PrismAudio feature extraction")