fix(review): validate skill roots at mount and isolate provider default roots

ds-review-bot round 1 on the repository-plugin runtime:
- a manifest-declared skill root absent or non-directory in the installed
  package now fails the plugin load (skill-local treats a missing root as
  legitimately empty, which silently mounted a skill-less plugin)
- includeDefaultRoots: false no longer inherits $DSH_BUNDLED_SKILL_DIR, so
  isolated repository providers see only their explicit roots
- prepared wrapper baseUrl schema requires the file: scheme, failing hostile
  URLs at the declared validation boundary
- preparedPath reuses format.ts's isOutside; SERVER_NAME_PATTERN is exported
  and pinned equal to dsh-mcp-client's, with the restatement justified (the
  prepare bin keeps a zod-only module graph); the unexplained `as never`
  cast now carries its schemastery rationale
- the import-free wrapper assertion also rejects dynamic import(
- the headless fixture wrapper is regenerated by the real prepareDshPlugin
  and a drift test pins fixture == generator output
- prepareDshPlugin JSDoc states the non-atomic publish repair contract

packages/cordis/repository-plugin/README.zh.md

@@ -36,7 +36,7 @@
 
 ## 运行时组合
 
-加载本包会注册一个 effect-scoped Loader builtin。每个生成的包装模块都把自身模块 URL 和已准备的 manifest 委托给该 builtin。Repository skill 根以唯一命名的 `dsh-skill-local` 提供方挂载，排除默认项目／用户根并禁用监视；缓存 package generation 是不可变的。包装模块 dispose 时，会通过正常的 Cordis 子 fiber teardown 移除提供方和所有组合的 MCP client。
+加载本包会注册一个 effect-scoped Loader builtin。每个生成的包装模块都把自身模块 URL 和已准备的 manifest 委托给该 builtin。运行时在挂载前会校验每个声明的 skill 根都是包内实际存在的目录——生成输出被丢弃的包（`files`／`.npmignore` 配置失误、缓存条目损坏）会使插件加载失败，而不是静默挂载一个没有 skill 的插件。Repository skill 根以唯一命名的 `dsh-skill-local` 提供方挂载，排除默认项目／用户根并禁用监视；缓存 package generation 是不可变的。包装模块 dispose 时，会通过正常的 Cordis 子 fiber teardown 移除提供方和所有组合的 MCP client。
 
 ## 通用 MCP 格式