chore(core-internal): cut the skills note on the barrel to one line

The repository keeps inline comments to one line; the reasoning (skills on the root barrel put the frontmatter parser in every package's root module graph) is in 7ee8d91's message.

Author: KKonstantinov

packages/core-internal/src/index.ts

@@ -1,11 +1,7 @@
 export * from './auth/errors';
 export * from './errors/crossBundleBrand';
 export * from './errors/sdkErrors';
-// The Skills extension's internals (SEP-2640) are deliberately NOT on this barrel:
-// they live on the `./ext/skills` subpath, so only the client and server
-// `ext/skills` entries load the frontmatter parser and the
-// `@modelcontextprotocol/core/ext/skills` import (on this barrel they landed in
-// every package's root module graph).
+// Skills internals live on the `./ext/skills` subpath, not here, so package roots never load them.
 export * from './shared/auth';
 export * from './shared/authUtils';
 export * from './shared/clientCapabilityRequirements';