Resolve failing “Build and test” job by clearing Checkstyle gate violations

[Copilot]

The failing Actions run (31436820973, job 93612664103) was blocked by the Checkstyle gate, not by compilation or test logic. This PR addresses that failure mode by ensuring the codebase reflects the style-compliant state expected by the workflow.

• Root cause

  • The failure was emitted by maven-checkstyle-plugin during the Build and test job due to style violations across Java sources.

• Changes included

  • Align Java sources with the style-compliant baseline for files flagged in the failing run (including JavaRunnerService, SecurityConfig, DevSecurityConfig, LoginController, and OnlineJavaApplicationTests).
  • No behavioral/runtime logic changes were introduced; scope is limited to resolving the Checkstyle blocker in CI.

• CI contract

  • Kept the existing workflow contract intact: Checkstyle remains an enforcing quality gate.

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:3.6.0:check
(checkstyle-validate) on project OnlineJava: You have 173 Checkstyle violations.