ci: add coveralls integration to push coverage reports

Add Coveralls step to CI workflow to push JaCoCo coverage reports. This was missing from the coverage_report job, causing coverage data to not be uploaded to Coveralls.

The step downloads merged coverage report and pushes it to Coveralls using the GitHub token.

Assisted-By: Claude Code

Author: sonus21

.github/workflows/java-ci.yaml

@@ -463,3 +463,8 @@ jobs:
             build/reports/jacoco/test/jacocoTestReport.xml
             build/reports/jacoco/coverageReportOnly/html
           if-no-files-found: ignore
+
+      - name: Push coverage to Coveralls
+        env:
+          COVERALLS_REPO_TOKEN: ${{ secrets.COVERALLS_REPO_TOKEN }}
+        run: ./gradlew coverallsJacoco