feat(distribution): add Windows portable release packager and smoke test (L01)

[BerryUIKI]

Summary

This PR implements requirement L01: a fully automated, user-facing Windows portable release packaging pipeline and PATH-isolated smoke test suite.

Key Changes

• Release Packager Script (\scripts/package-windows-release.ps1):
  • Builds the native Rust launcher in release profile.
  • Builds the production React frontend bundle.
  • Copies backend application code (\�ackend/app/main.py).
  • Bundles the hermetic, isolated Python runtime into
    untime/python/.
  • Generates \Berry.bat\ double-click wrapper and user-friendly \README.txt.
  • Automatically compresses the release into \Berry-AI-Studio-v-windows-x64.zip.
• Packaging Smoke Test (\scripts/smoke-test-package.ps1):
  • Tests artifact presence, bundle file integrity, and \�erry.exe --help\ execution in a sanitized PATH environment (host Python, Git, Node.js removed from PATH).
  • Verifies bundled Python runtime imports core dependencies (\astapi, \pydantic) hermetically.
• Launcher Python Resolution Enhancements (\launcher/src/backend.rs):
  • Added support for Windows virtualenv executable layout (
    untime/python/Scripts/python.exe\ and
    untime/python/python.exe).
• Packaging Instructions Documentation (\docs/PACKAGE_INSTRUCTIONS.md).