ci: enable coveralls debug output to diagnose request payload

Write coveralls request JSON to file for debugging and display it in CI
logs so we can see exactly what data is being sent to Coveralls API.

Assisted-By: Claude Code

Author: sonus21

.github/workflows/java-ci.yaml

@@ -478,3 +478,9 @@ jobs:
             exit 1
           fi
           ./gradlew coverallsJacoco
+          echo "=== Coveralls request payload ==="
+          if [ -f build/coveralls-request.json ]; then
+            cat build/coveralls-request.json | head -100
+          else
+            echo "No coveralls-request.json file found"
+          fi

build.gradle

@@ -206,6 +206,8 @@ coverallsJacoco {
     reportSourceSets = publishedProjects.collectMany {
         it.sourceSets.main.allSource.srcDirs
     }
+    // Debug: write request payload to file to see what's being sent
+    coverallsRequest = file("build/coveralls-request.json")
 }
 
 def javaFormatSources = providers.provider {