FullTextSearch + LoadByGuids could stall the draw thread for 100-300 ms
on large databases with a popular search term. The two hot trigger sites
(FTS toggle, search input) now route via TriggerFilterRefresh, which
dispatches the FTS path to Task.Run; the in-memory page-filter path
stays inline because it is sub-ms on the loaded page array.
_ftsFilterSeq is bumped per trigger so a late worker recognises itself
as stale and drops its result instead of overwriting a newer one. The
date/channel and history workers already lived on Task.Run and are
untouched.
Surfaced during the v1.4.8 pre-tag review.
JonKazama-Hellion
7542d48983