v1.6.8

feat: clean up settings, add database maintenance, improve export

- Remove E→L Search Engine checkboxes from Settings (now in Sidebar)
- Add Database Maintenance section in Database tab (Rebuild FTS, Compact DB)
- Fix delete_word to auto-rebuild FTS after cascade delete
- Add compact_db command (SQLite VACUUM)
- Add wildcard toggle in Sidebar List settings
- Fix event filter in HTML export to include all words available at event
- Add event label to exported HTML sidebar
- Make Clear Type Filter button larger on mobile