fix(ci): install client from release branch before uv sync (#4002)

Backport of #4001 to release-0.3.x branch.

Fixes CI failures on release branches where uv sync can't resolve RC
dependencies.

## The Problem

On release branches like `release-0.3.x`, pyproject.toml requires
`llama-stack-client>=0.3.1rc1`. RC versions only exist on test.pypi, not
PyPI. This causes multiple CI failures:

1. `uv sync` fails because it can't resolve RC versions from PyPI
2. pre-commit hooks (uv-lock, codegen) fail for the same reason  
3. mypy workflow section needs uv installed

## The Solution

Configure UV to use test.pypi when on release branches:

- Set `UV_INDEX_URL=https://test.pypi.org/simple/` (primary)
- Set `UV_EXTRA_INDEX_URL=https://pypi.org/simple/` (fallback)
- Set `UV_INDEX_STRATEGY=unsafe-best-match` to check both indexes

This allows `uv sync` to resolve common packages from PyPI and RC
versions from test.pypi.

## Additional Fixes

- Export UV env vars to `GITHUB_ENV` so pre-commit hooks inherit them
- Install uv in pre-commit workflow for mypy section
- Handle missing `type_checking` dependency group on release-0.3.x
- Regenerate uv.lock with RC versions for the release branch

## Changes

- Created reusable `install-llama-stack-client` action for configuration
- Modified `setup-runner` to set UV environment variables before sync
- Modified `pre-commit` workflow to configure client and export env vars
- Updated uv.lock with RC versions from test.pypi

This is a cherry-pick of commits afa9f0882, c86e6e906, 626639bee, and
081566321 from main, plus additional fixes for release branch
compatibility.

.github/actions/setup-test-environment/action.yml

@@ -42,29 +42,7 @@ runs:
     - name: Build Llama Stack
       shell: bash
       run: |
-        # Install llama-stack-client-python based on the client-version input
-        if [ "${{ inputs.client-version }}" = "latest" ]; then
-          # Check if PR is targeting a release branch
-          TARGET_BRANCH="${{ github.base_ref }}"
-
-          if [[ "$TARGET_BRANCH" =~ ^release-[0-9]+\.[0-9]+\.x$ ]]; then
-            echo "PR targets release branch: $TARGET_BRANCH"
-            echo "Checking if matching branch exists in llama-stack-client-python..."
-
-            # Check if the branch exists in the client repo
-            if git ls-remote --exit-code --heads https://github.com/llamastack/llama-stack-client-python.git "$TARGET_BRANCH" > /dev/null 2>&1; then
-              echo "Installing llama-stack-client-python from matching branch: $TARGET_BRANCH"
-              uv pip install --force-reinstall git+https://github.com/llamastack/llama-stack-client-python.git@$TARGET_BRANCH
-            else
-              echo "::error::Branch $TARGET_BRANCH not found in llama-stack-client-python repository"
-              echo "::error::Please create the matching release branch in llama-stack-client-python before testing"
-              exit 1
-            fi
-          fi
-          # For main branch, client is already installed by setup-runner
-        fi
-        # For published version, client is already installed by setup-runner
-
+        # Client is already installed by setup-runner via install-llama-stack-client action
         echo "Building Llama Stack"
 
         LLAMA_STACK_DIR=. \