ci(coverage): include coverage log in artifact upload

The birpc guard step writes to /tmp/coverage-test-<run_id>.log and exits 1
when a race is detected. Without this file in the artifact, the evidence
disappears when the runner tears down — only the exit code remained visible.

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

.gitea/workflows/ci.yml

@@ -66,7 +66,9 @@ jobs:
         uses: actions/upload-artifact@v4
         with:
           name: coverage-reports
-          path: frontend/coverage/
+          path: |
+            frontend/coverage/
+            /tmp/coverage-test-${{ github.run_id }}.log
 
       - name: Build frontend
         run: npm run build