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

docs/config-catalog.md

@@ -867,7 +867,7 @@ export interface StreamableHttpConfig {
 }
 ```
 
-Source: [`packages/mcp/mcp-client/src/index.ts:93`](../packages/mcp/mcp-client/src/index.ts)
+Source: [`packages/mcp/mcp-client/src/index.ts:96`](../packages/mcp/mcp-client/src/index.ts)
 
 ## `@deepseek-ai/dsh-permission`
 
@@ -1334,7 +1334,7 @@ export interface Config {
   watchMaxProjects?: number
   /** Whether watched symbolic links follow their target files. */
   watchFollowSymlinks?: boolean
-  /** Bundled skill root; defaults to `$DSH_BUNDLED_SKILL_DIR`, otherwise mounts none. */
+  /** Bundled skill root; defaults to `$DSH_BUNDLED_SKILL_DIR` when default roots are included, otherwise mounts none. */
   bundledSkillDir?: string
 }
 ```