feat(workbench): migrate the local workspace to FastAPI and React

[tiammomo]

Closes #131

默认安装后继续用 reposteward web 启动 FastAPI 同源服务，React 页面完整提供现有读取流程；OpenAPI 生成 TypeScript 类型，安装 wheel 无需源码目录或 Node，公开写入仍使用既有原生门禁。

---

用户已确认技术选型与实施授权。本Issue范围是新框架工作台的完整迁移与分发，后续GitHub同步/终态分类、已有项目三路径导入、持久操作及任务聚合分别进入聚焦Issue。本次保留现有只读业务语义，新增/api/v1类型契约与兼容读取适配；前端采用项目导航与组件结构，保留既有读取和复制能力。新操作只在后续能力真实实现后出现。

Verified with uvx ruff check ., uvx ruff format --check ., uv run --python 3.12 python -W error::ResourceWarning -m unittest discover -s tests -v, uv run reposteward --help, uv build.

Areas for careful review:

• No known behavior changes outside the reported bug.

Implementation assistance: an external coding workspace was used to prepare the change and its
tests. tiammomo reviewed the final diff, understands it, and takes responsibility
for this contribution.