refactor(examples): remove Lombok from graceful-shutdown module

[YunKuiLu]

Summary

• Remove lombok dependency from agentscope-examples/graceful-shutdown/pom.xml
• Replace @Slf4j annotation with manual LoggerFactory.getLogger() declaration in AgentService.java

Motivation

The graceful-shutdown example module declared a dependency on Lombok (org.projectlombok:lombok), which caused compilation failure for projects that do not have Lombok configured in their IDE or build environment (no annotation processor setup). This created an unnecessary barrier for users trying to build the examples.

Verification

• Module contains zero remaining Lombok references
• log variable name unchanged — all 4 call sites (log.info, log.warn) work without modification
• SLF4J is already available as a transitive dependency via spring-boot-starter-web

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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