Fix CI for Gitea act_runner: python3 and local docker build.

Use python3 instead of unavailable python3.11 packages, drop apt step that failed on runner image, and replace buildx with docker build so the test step can run the built image.

.github/workflows/ci.yml

@@ -28,15 +28,10 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v4
 
-      - name: Install system dependencies
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y postgresql-client python3.11 python3.11-venv python3-pip
-
       - name: Install Python dependencies
         run: |
-          pip install --upgrade pip
-          pip install -e ".[dev]"
+          python3 -m pip install --upgrade pip
+          python3 -m pip install -e ".[dev]"
 
       - name: Run linters
         run: |
@@ -56,7 +51,7 @@ jobs:
           SMTP_PASSWORD: ${{ secrets.SMTP_PASSWORD || 'dummy' }}
           FROM_EMAIL: ${{ secrets.FROM_EMAIL || 'test@example.com' }}
         run: |
-          pytest tests/ -v --cov=src/pote --cov-report=term --cov-report=xml
+          python3 -m pytest tests/ -v --cov=src/pote --cov-report=term --cov-report=xml
 
       - name: Test scripts
         env:
@@ -75,19 +70,19 @@ jobs:
 
       - name: Install dependencies
         run: |
-          python3.11 -m pip install --upgrade pip
-          python3.11 -m pip install safety bandit
+          python3 -m pip install --upgrade pip
+          python3 -m pip install safety bandit
 
       - name: Run safety check
         run: |
-          python3.11 -m pip install -e .
-          python3.11 -m safety check --json || true
+          python3 -m pip install -e .
+          python3 -m safety check --json || true
         continue-on-error: true
 
       - name: Run bandit security scan
         run: |
-          python3.11 -m bandit -r src/ -f json -o bandit-report.json || true
-          python3.11 -m bandit -r src/ -f screen
+          python3 -m bandit -r src/ -f json -o bandit-report.json || true
+          python3 -m bandit -r src/ -f screen
         continue-on-error: true
 
   dependency-scan:
@@ -111,20 +106,10 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v4
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
-      - name: Build Docker image
-        uses: docker/build-push-action@v5
-        with:
-          context: .
-          push: false
-          tags: pote:test
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
-
-      - name: Test Docker image
+      - name: Build and test Docker image
         run: |
+          # Plain docker build — buildx images are not visible to act_runner's docker run
+          docker build -t pote:test .
           docker run --rm pote:test python -c "import pote; print('POTE import successful')"
 
   workflow-summary: