npm workspaces hoists example dependencies to the root node_modules,
but installs the published registry copy of @modelcontextprotocol/ext-apps
instead of linking to the local source. This causes type-check failures
when examples use features not yet published to npm.
Add scripts/link-self.mjs which copies the freshly-built dist/ and
package.json into the hoisted node_modules copy after each SDK build,
ensuring examples always type-check against the latest local types.
See: https://github.com/npm/feedback/discussions/774
