ci: add notify-failure, deploy tagging, and coverage reporting

- lint.yml: add notify-failure Matrix alert job; add Tag deployed commit
  step to deploy job with deploy-YYYY.MM.DD-N tagging via Gitea API
- test.yml: add pytest-cov for coverage reporting
- .coveragerc: omit tests and site-packages from coverage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/test.yml

@@ -17,8 +17,8 @@ jobs:
         run: |
           apt-get update -qq
           apt-get install -y -qq python3 python3-pip
-          pip3 install pytest
+          pip3 install pytest pytest-cov
           pip3 install -r requirements.txt --quiet
 
-      - name: Run pytest
-        run: python3 -m pytest tests/ -v
+      - name: Run pytest with coverage
+        run: python3 -m pytest tests/ -v --cov=. --cov-report=term-missing --cov-config=.coveragerc