refactor: consolidate all client install logic into single action

Renamed install-client-for-release to install-llama-stack-client and
made it handle both release branches and client-version inputs. Now
all client installation logic lives in one place:

- Release branches: always install from matching git branch
- Non-release branches: install based on client-version input

This eliminates all the conditional logic from setup-runner.

.github/actions/install-llama-stack-client/action.yml

@@ -0,0 +1,51 @@
+name: Install llama-stack-client
+description: Install llama-stack-client based on branch context and client-version input
+
+inputs:
+  client-version:
+    description: 'Client version to install on non-release branches (latest or published). Ignored on release branches.'
+    required: false
+    default: ""
+
+runs:
+  using: "composite"
+  steps:
+    - name: Install llama-stack-client
+      shell: bash
+      run: |
+        # Determine the branch we're working with
+        # For PRs: use base_ref (target branch)
+        # For pushes: use ref (current branch)
+        BRANCH="${{ github.base_ref || github.ref }}"
+        BRANCH="${BRANCH#refs/heads/}"  # Strip refs/heads/ prefix
+
+        echo "Working with branch: $BRANCH"
+
+        # On release branches: always install from matching git branch to satisfy RC dependencies
+        # On non-release branches: install based on client-version input
+        if [[ "$BRANCH" =~ ^release-[0-9]+\.[0-9]+\.x$ ]]; then
+          echo "Detected release branch: $BRANCH"
+          echo "Checking if matching branch exists in llama-stack-client-python..."
+
+          # Check if the branch exists in the client repo
+          if git ls-remote --exit-code --heads https://github.com/llamastack/llama-stack-client-python.git "$BRANCH" > /dev/null 2>&1; then
+            echo "Installing llama-stack-client-python from matching branch: $BRANCH"
+            uv pip install git+https://github.com/llamastack/llama-stack-client-python.git@$BRANCH
+          else
+            echo "::error::Branch $BRANCH not found in llama-stack-client-python repository"
+            echo "::error::Please create the matching release branch in llama-stack-client-python before testing"
+            exit 1
+          fi
+        elif [ -n "${{ inputs.client-version }}" ]; then
+          # Non-release branch with client-version specified
+          if [ "${{ inputs.client-version }}" = "latest" ]; then
+            echo "Installing latest llama-stack-client-python from main branch"
+            uv pip install git+https://github.com/llamastack/llama-stack-client-python.git@main
+          elif [ "${{ inputs.client-version }}" = "published" ]; then
+            echo "Installing published llama-stack-client-python from PyPI"
+            uv pip install llama-stack-client
+          else
+            echo "Invalid client-version: ${{ inputs.client-version }}"
+            exit 1
+          fi
+        fi