lance serves unsorted results with matching rows dropped when a
declared FTS index has indexed nothing, or when a populated table has
no FTS index at all. doctor fails on both: vacuum remediation for an
existing index, rebuild --embed-only for a missing one, since optimize
never creates an index. The chunk repository warns once per repository
on the first FTS or hybrid search against either state; a failing
coverage check is logged and never fails the search. Removes
_ensure_fts_index, which had no callers.
61df6b65a6