refactor(desktop): shell polish — register the dsh launcher, use vendored pnpm, docs

Register the dsh CLI launcher from the desktop shell, prefer the vendored
pnpm in the CLI plugin command, and update the desktop and CLI reference docs.

Co-Authored-By: Claude <noreply@anthropic.com>

packages/boot/app-boot/src/index.ts

@@ -41,6 +41,7 @@ export {
   readProfileManifest,
   reconcileProfileBundles,
   resolveBundleDir,
+  resolvePnpm,
   resolveProfileDir,
   writeProfileManifest,
   type DshBundleManifest,