Backport UV index configuration fixes from release-0.3.x that enable
resolution of RC dependencies from test.pypi while keeping PyPI as the
primary index.
Key changes:
- Fix install-llama-stack-client action to use test.pypi as EXTRA index
(not primary) to prevent UV from looking for all packages there first
- Add uv-run-with-index.sh wrapper that auto-detects release branches
and sets UV env vars for local pre-commit hooks
- Update pre-commit hooks to use the wrapper for all uv commands
- Add UV_INDEX_STRATEGY=unsafe-best-match to allow checking multiple indexes
- Pass UV env vars as Docker build args and use them inline only for
llama-stack installation to avoid affecting distribution deps
- Export UV env vars to GITHUB_ENV in setup-runner for cross-step persistence
This infrastructure allows future release branches to work correctly
without manual UV configuration.
