Add reusable local HTTP job service for Blender add-ons

- Implement JobClient for handling HTTP requests to the JobServer.
- Create ModalJobOperatorBase for managing Blender job lifecycle.
- Introduce JobContext and JobServer for job management and state handling.
- Add ServiceConnection and ServiceController for managing service processes.
- Implement job submission, cancellation, and resource management endpoints in the server.
- Ensure proper error handling and job state updates throughout the service.

docs/index.md

@@ -7,4 +7,5 @@
 - [Surface](surface.md)：透视网格、Geometry Nodes 后处理与材质法线
 - [输出格式](outputs.md)：Debug 输出类型、参数和任务产物
 - [AI Service](service.md)：Environment、模型缓存、任务目录与运行机制
+- [BlendJob 开发者指南](blendjob.md)：可复用 Job Server、Blender Client 与装饰器注册 API
 - [开发与许可证](development.md)：开发验证、打包、上游版本与许可证