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.

scripts/uv-run-with-index.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+set -euo pipefail
+
+# Detect current branch and target branch
+# In GitHub Actions, use GITHUB_REF/GITHUB_BASE_REF
+if [[ -n "${GITHUB_REF:-}" ]]; then
+  BRANCH="${GITHUB_REF#refs/heads/}"
+else
+  BRANCH=$(git rev-parse --abbrev-ref HEAD 2>/dev/null || echo "")
+fi
+
+# For PRs, check the target branch
+if [[ -n "${GITHUB_BASE_REF:-}" ]]; then
+  TARGET_BRANCH="${GITHUB_BASE_REF}"
+else
+  TARGET_BRANCH=$(git rev-parse --abbrev-ref HEAD@{upstream} 2>/dev/null | sed 's|origin/||' || echo "")
+fi
+
+# Check if on a release branch or targeting one, or LLAMA_STACK_RELEASE_MODE is set
+IS_RELEASE=false
+if [[ "$BRANCH" =~ ^release-[0-9]+\.[0-9]+\.x$ ]]; then
+  IS_RELEASE=true
+elif [[ "$TARGET_BRANCH" =~ ^release-[0-9]+\.[0-9]+\.x$ ]]; then
+  IS_RELEASE=true
+elif [[ "${LLAMA_STACK_RELEASE_MODE:-}" == "true" ]]; then
+  IS_RELEASE=true
+fi
+
+# On release branches, use test.pypi as extra index for RC versions
+if [[ "$IS_RELEASE" == "true" ]]; then
+  export UV_EXTRA_INDEX_URL="https://test.pypi.org/simple/"
+  export UV_INDEX_STRATEGY="unsafe-best-match"
+fi
+
+# Run uv with all arguments passed through
+exec uv "$@"