fix(stats): serialize excluded word writes to avoid races

- Queue setExcludedWords writes so a slower in-flight save can't land after and overwrite a newer edit
- Run server-sync listeners independently so one throwing listener doesn't roll back a successful write or block the rest
- Add regression tests for write ordering, listener isolation, coalesced known-word snapshots, and vocabulary hook aggregate refresh/retry

changes/stats-vocabulary-summary-totals.md

@@ -5,3 +5,4 @@ area: stats
 - New-word history now uses permanent daily lexical rollups, backfilled in the background and repaired when tracked material is removed or reprocessed; playback writes queue safely during the one-time rebuild and resume afterward.
 - Calendar-day chart labels now preserve the recorded local date in time zones west of UTC.
 - Vocabulary summary cards and charts refresh automatically after the word exclusion list changes, and failed loads retry with backoff before showing an inline error with a Retry control.
+- Rapid exclusion edits no longer race each other; writes are sent in order so a slower earlier save cannot overwrite a newer list.