ci: mobile-friendly test results via GitHub Actions

Workflow upgrades:
- permissions: checks: write + pull-requests: write (required for annotations)
- pytest now outputs --junitxml=reports/junit.xml and --cov-report=xml
- EnricoMi/publish-unit-test-result-action@v2: posts a "pytest results"
  check annotation AND a PR comment showing pass/fail counts with
  per-test breakdown — both visible in the GitHub mobile app
- actions/upload-artifact@v4: uploads coverage.xml (14-day retention)
  browsable from the Actions tab on mobile

README:
- Live test badge at the top (green/red, links to Actions run history)

.gitignore:
- Add reports/ so generated junit.xml + coverage.xml are never committed

https://claude.ai/code/session_01M4L3R98N5fgXFZRvV8X9b6

.github/workflows/tests.yml

@@ -10,6 +10,12 @@ jobs:
   test:
     runs-on: ubuntu-latest
 
+    # Required for publish-unit-test-result-action to post check runs and PR comments
+    permissions:
+      contents: read
+      checks: write
+      pull-requests: write
+
     steps:
       - uses: actions/checkout@v4
 
@@ -22,4 +28,30 @@ jobs:
         run: pip install -e ".[dev]"
 
       - name: Run tests
-        run: pytest --cov=src --cov-report=term-missing
+        run: |
+          pytest \
+            --tb=short \
+            --cov=src \
+            --cov-report=term-missing \
+            --cov-report=xml:reports/coverage.xml \
+            --junitxml=reports/junit.xml
+
+      # Posts a check annotation + PR comment showing pass/fail counts.
+      # Visible in the GitHub mobile app under Checks and in PR conversations.
+      - name: Publish test results
+        uses: EnricoMi/publish-unit-test-result-action@v2
+        if: always()
+        with:
+          files: reports/junit.xml
+          check_name: "pytest results"
+          comment_title: "Test Results"
+          report_individual_runs: true
+
+      # Coverage report available as a downloadable artifact in the Actions tab
+      - name: Upload coverage report
+        uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: coverage-report
+          path: reports/coverage.xml
+          retention-days: 14