chore(sdk): drop dsh-plugin-fetch (giget/pacote) — #2 will use native npm/pnpm deps

External-plugin creation will add a package-manager-native dependency
(github:owner/repo#ref or pkg@version) plus a cordis mount instead of fetching
tarballs into a temp dir, so the giget/pacote fetch package is no longer needed.

scripts/verify-package-readme-model-experience.ts

@@ -52,7 +52,6 @@ const SENTENCE_MODEL_EXPERIENCE: Readonly<Record<string, SentenceContract>> = {
   'packages/sandbox/sandbox-local': { kind: 'indirect', reason: 'The provider backend delegates model rendering to dsh-bash-sandbox and dsh-tool-bash.' },
   'packages/sdk/create-sdk': { kind: 'indirect', reason: 'The initializer only writes project files; selected runtime plugins provide the generated project model surface.' },
   'packages/sdk/helper': { kind: 'none', reason: 'The project domain edits files and registers no live agent or model surface.' },
-  'packages/sdk/plugin-fetch': { kind: 'none', reason: 'The fetcher acquires plugin sources into a temp dir and registers no live agent or model surface.' },
   'packages/sdk/scripts': { kind: 'indirect', reason: 'The launcher delegates model context to the loaded project plugin tree.' },
   'packages/sdk/telemetry': { kind: 'none', reason: 'The launcher-side reporter sends developer-cycle telemetry and registers no live agent or model surface.' },
   'packages/session-query/session-query': { kind: 'none', reason: 'The trusted query service exposes cloned records only to callers and registers no model surface.' },