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/tests.yml

@@ -11,17 +11,17 @@ jobs:
     name: Code Quality (Ruff & Mypy)
     runs-on: ubuntu-latest
     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'
 
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install ruff mypy
+        pip install "ruff>=0.15" mypy
         pip install -e .
 
     - name: Run ruff linter
@@ -53,12 +53,12 @@ jobs:
             python-version: '3.10'
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         submodules: recursive  # Initialize api/configs_repo submodule
 
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
 
@@ -68,7 +68,7 @@ jobs:
         echo "$HOME/.local/bin" >> $GITHUB_PATH
 
     - name: Cache pip packages
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ~/.cache/pip
         key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt', 'skill_seeker_mcp/requirements.txt') }}
@@ -98,7 +98,7 @@ jobs:
         python -m pytest tests/ --cov=src/skill_seekers --cov-report=xml --cov-report=term
 
     - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
       with:
         file: ./coverage.xml
         flags: unittests