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/workflows/install-script-ci.yml

@@ -30,10 +30,16 @@ jobs:
 
       - name: Build a single provider
         run: |
+          BUILD_ARGS="--build-arg INSTALL_MODE=editable --build-arg DISTRO_NAME=starter"
+          if [ -n "${UV_EXTRA_INDEX_URL:-}" ]; then
+            BUILD_ARGS="$BUILD_ARGS --build-arg UV_EXTRA_INDEX_URL=$UV_EXTRA_INDEX_URL"
+          fi
+          if [ -n "${UV_INDEX_STRATEGY:-}" ]; then
+            BUILD_ARGS="$BUILD_ARGS --build-arg UV_INDEX_STRATEGY=$UV_INDEX_STRATEGY"
+          fi
           docker build . \
             -f containers/Containerfile \
-            --build-arg INSTALL_MODE=editable \
-            --build-arg DISTRO_NAME=starter \
+            $BUILD_ARGS \
             --tag llama-stack:starter-ci
 
       - name: Run installer end-to-end