feat: auto-install pip venv for feature extraction on first use

PrismAudioFeatureExtractor now creates and populates a managed venv
(_extract_env/) automatically when python_env is left as the default
'python'. Also adds scripts/install_extract_env.sh for manual/Docker
setup without conda.

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

scripts/install_extract_env.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Install the PrismAudio feature-extraction environment using pip venv.
+# Use this instead of environment.yml when conda is unavailable (e.g. NVIDIA Docker).
+#
+# Usage:
+#   bash scripts/install_extract_env.sh [/path/to/venv]
+#
+# Default venv path: /opt/prismaudio-extract
+# After installation, point the PrismAudioFeatureExtractor node's python_env to:
+#   <venv>/bin/python   (Linux/Mac)
+#   <venv>\Scripts\python.exe  (Windows)
+
+set -euo pipefail
+
+VENV_DIR="${1:-/opt/prismaudio-extract}"
+
+echo "[PrismAudio] Creating venv at: ${VENV_DIR}"
+python3 -m venv "${VENV_DIR}"
+
+PIP="${VENV_DIR}/bin/pip"
+
+echo "[PrismAudio] Upgrading pip..."
+"${PIP}" install --upgrade pip
+
+echo "[PrismAudio] Installing PyTorch stack..."
+"${PIP}" install torch torchaudio torchvision
+
+echo "[PrismAudio] Installing feature-extraction dependencies..."
+"${PIP}" install \
+    "tensorflow-cpu==2.15.0" \
+    "jax[cpu]" \
+    "jaxlib" \
+    "transformers" \
+    "decord" \
+    "einops" \
+    "numpy" \
+    "mediapy"
+
+echo "[PrismAudio] Installing VideoPrism..."
+"${PIP}" install "git+https://github.com/google-deepmind/videoprism.git"
+
+echo ""
+echo "[PrismAudio] Done. Set python_env in PrismAudioFeatureExtractor to:"
+echo "  ${VENV_DIR}/bin/python"