feat: cross-runner molecule cancellation via Gitea API polling

Gitea Actions does not implement fail-fast/max-parallel for matrix jobs,
so a failing runner does not stop the others. Added molecule_ci_guard.py
which polls the Gitea API in a background thread. If any other molecule
runner reports failure, the current runner kills its molecule subprocess
and exits early.

CI returns to a 3-runner matrix; each runner executes its assigned pairs
in parallel via run_molecule_parallel.py, guarded by molecule_ci_guard.py.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.gitea/workflows/ci.yml

@@ -29,16 +29,28 @@ jobs:
   molecule-tests:
     needs: quality
     runs-on: docker
+    strategy:
+      matrix:
+        runner-index: [0, 1, 2]
     steps:
       - uses: actions/checkout@v4
       - name: Set up environment
         run: make setup
-      - name: Run all molecule tests in parallel
+      - name: Discover assigned test pairs
+        run: |
+          . .venv/bin/activate
+          PAIRS=$(python3 scripts/distribute_molecule.py --runner-index ${{ matrix.runner-index }} --max-runners 3)
+          echo "Assigned pairs: $PAIRS"
+          echo "TEST_PAIRS=$PAIRS" >> $GITHUB_ENV
+      - name: Run molecule tests
         run: |
           set -euo pipefail
           . .venv/bin/activate
-          export DOCKER_HOST="unix:///run/user/$(id -u)/docker.sock"
-          export ANSIBLE_INJECT_INVOCATION=1
-          PAIRS=$(python3 scripts/distribute_molecule.py --runner-index 0 --max-runners 1)
-          echo "Running all pairs in parallel: $PAIRS"
-          python3 scripts/run_molecule_parallel.py $PAIRS
+          python3 scripts/molecule_ci_guard.py $TEST_PAIRS
+        env:
+          GITEA_URL: ${{ github.server_url }}
+          REPO_TOKEN: ${{ secrets.REPO_TOKEN }}
+          RUN_ID: ${{ github.run_id }}
+          JOB_NAME: ${{ github.job }}
+          MATRIX_INDEX: ${{ matrix.runner-index }}
+          GITEA_REPOSITORY: ${{ github.repository }}