Revisit: getMongoClient() JSDoc is misleading; only used by main thread scanCollectionSchema

Context

ClustersClient.getMongoClient() has a JSDoc that says:

Used by the query playground evaluator to create a @mongosh ServiceProvider that reuses the existing, authenticated connection.

In practice the playground worker has its own MongoClient (different Node worker_thread, separate V8 isolate). The only caller of getMongoClient() is src/commands/playground/scanCollectionSchema.ts which runs in the extension host (main thread). The JSDoc is misleading.

Suggested solutions

1. Update the JSDoc to reflect the real caller: schema scan from the extension host.
2. Consider whether exposing the raw MongoClient is necessary at all, or whether a narrower API on ClustersClient (for example getCollection(db, coll)) would be safer to expose.

Definition of done

• JSDoc accurately reflects the caller.
• Optional: scope of the public API surface is reduced.

Start in src/documentdb/ClustersClient.ts and inspect the getMongoClient() JSDoc, then read its only named caller, src/commands/playground/scanCollectionSchema.ts. Update the documentation to describe the extension-host schema scan accurately and assess whether the suggested narrower API is needed; done means the JSDoc matches actual usage and any API-scope decision is recorded.