fix: upgrade deprecated GitHub Actions to v4/v5 and fix MCP test job

actions/upload-artifact@v3 is fully deprecated and causes instant CI
failure. Also upgrades checkout, setup-python, cache, github-script,
and codecov actions to their latest major versions to resolve Node.js 20
deprecation warnings. Adds missing pytest install to MCP Vector DB test
job and pins ruff>=0.15 in CI to match local tooling.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/docker-publish.yml

@@ -44,7 +44,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v2
@@ -100,7 +100,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Build CLI image
       run: |