feat(agui): CopilotKit demo and HITL interrupt resume fixes

[dragondyt]

Summary

• Add a full-stack CopilotKit + AG-UI example (agentscope-copilotkit) to verify threads, shared state, generative UI, A2UI workbench, and HITL flows end-to-end.
• Extend ThreadSessionManager so demo/session APIs can ensure named sessions and correctly resolve memory by threadId.

Depends on

• Depends on fix(agui): parse request bodies with Jackson 2 codec #2638 (Jackson 2 request-body parsing for Boot 4 / multimodal MessageContent). Merge fix(agui): parse request bodies with Jackson 2 codec #2638 first, or keep this PR stacked on top of it.

Related issues

• Related to [Feature]: copilotkit uses the agui protocol to call agentscope-java unrecognized context #575
• Related to [Feature]: Integrate AG-UI with Session #336

Test plan

• mvn spotless:check on example / agui-spring-boot-starter
• ThreadSessionManagerTest
• mvn -pl agentscope-examples/agentscope-copilotkit package (npm frontend build + Spring Boot repackage)
• Manual: start agentscope-copilotkit backend + frontend, confirm HITL interrupt/resume, thread session, shared state, and generative UI flows

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../spring/boot/agui/common/ThreadSessionManager.java	87.50%	1 Missing and 4 partials ⚠️

📢 Thoughts on this report? Let us know!

[jujn]

建议拆分一下，当前PR仅保留 CopilotKit 示例项目即可。Permission Interrupt 工具目前已经支持了，其它的可以单开小PR。

[dragondyt]

OK，我会基于最新的main分支拆分一下

[dragondyt]

@jujn 已简化，仅保留 CopilotKit 示例项目，运行依赖pr: #2638