Three groups, not two: `search`, `ask`, `analyze` and `chat` cover the set,
`settings`, `init-config` and `download-models` open no database, and every
other command works on one — or on a configured set of one, which is
unambiguous and keeps its name. A database named in `lancedb.databases` keeps
that name whether or not it is the only one covered; only `lancedb.uri` places
one without naming it.
Document ids repeat between copies of a database, where the sandbox refuses a
duplicate but the chat filter's `id IN (...)` matches the document in every
copy. `build_document_id_filter` claimed ids never widen a selection.
Document the facade: `covers_multiple`, `source_names`, `source`,
`reader_for`, `clients_for`, the lifetime of a borrowed client, and
`sources=None` against `sources=[]`.
Drop the vision callout from the README, which the features list already
covers.