Create, update, tune, and inspect Collection-wide or Shard-local Topics (custom clusters) in an mdvdb vault: clusters add/update/remove/list/unassigned, per-Topic thresholds, independent Shard scopes, and clustering config via mdvdb config set. Use when the user wants to organize documents into Topics, color Tesseract's graph, tune a Topic, review Unassigned documents, or give a Shard/sub-collection its own Topics.
