refactor(colab): remove cd and use absolute paths for idempotent runs

- avoid stateful working-directory changes in notebook cells
- use explicit /content/... paths for clone/install/inference
- improves readability and re-run reliability

demo/VibeVoice_colab.ipynb

@@ -63,9 +63,6 @@
         "![ -d /content/VibeVoice ] || git clone --quiet --branch main --depth 1 https://github.com/microsoft/VibeVoice.git /content/VibeVoice\n",
         "print(\"✅ Cloned VibeVoice repository\")\n",
         "\n",
-        "# Go to repo directory\n",
-        "!cd /content/VibeVoice\n",
-        "\n",
         "# Install project dependencies\n",
         "!uv pip --quiet install --system -e /content/VibeVoice\n",
         "print(\"✅ Installed dependencies\")\n",