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/quality-metrics.yml

@@ -31,10 +31,10 @@ jobs:
       FAIL_THRESHOLD_INPUT: ${{ github.event.inputs.fail_threshold }}
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
 
     - name: Set up Python 3.12
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v5
       with:
         python-version: '3.12'
 
@@ -141,7 +141,7 @@ jobs:
         fi
 
     - name: Upload quality reports
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: quality-metrics-reports
         path: quality_*.txt
@@ -150,7 +150,7 @@ jobs:
 
     - name: Post summary to PR
       if: github.event_name == 'pull_request'
-      uses: actions/github-script@v6
+      uses: actions/github-script@v7
       with:
         script: |
           const fs = require('fs');