fix(ci): use test.pypi as extra index for RC dependencies

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.

.github/actions/setup-runner/action.yml

@@ -27,9 +27,16 @@ runs:
     - name: Install dependencies
       shell: bash
       env:
-        UV_INDEX_URL: ${{ steps.client-config.outputs.uv-index-url }}
         UV_EXTRA_INDEX_URL: ${{ steps.client-config.outputs.uv-extra-index-url }}
+        UV_INDEX_STRATEGY: ${{ steps.client-config.outputs.uv-extra-index-url && 'unsafe-best-match' || '' }}
       run: |
+        # Export UV env vars to GITHUB_ENV so they persist across steps
+        if [ -n "$UV_EXTRA_INDEX_URL" ]; then
+          echo "UV_EXTRA_INDEX_URL=$UV_EXTRA_INDEX_URL" >> $GITHUB_ENV
+          echo "UV_INDEX_STRATEGY=$UV_INDEX_STRATEGY" >> $GITHUB_ENV
+          echo "Exported UV environment variables for subsequent steps"
+        fi
+
         echo "Updating project dependencies via uv sync"
         uv sync --all-groups