fix(tokenizer): preserve known-word highlight when POS filters suppress

- Known-word cache matches now set isKnown=true even for tokens excluded by POS filters
- POS exclusion gate suppresses N+1, frequency, and JLPT only; known status is computed before the gate
- Jellyfin subtitle preload continues after cleanup failures instead of aborting
- Update config docs and option description to document the known-word bypass behavior

src/main/runtime/jellyfin-subtitle-preload.ts

@@ -246,7 +246,11 @@ export function createPreloadJellyfinExternalSubtitlesHandler(deps: {
     itemId: string;
   }): Promise<void> => {
     try {
-      cleanupActiveCache();
+      try {
+        cleanupActiveCache();
+      } catch (error) {
+        deps.logDebug('Failed to cleanup Jellyfin cached subtitles', error);
+      }
       const tracks = await deps.listJellyfinSubtitleTracks(
         params.session,
         params.clientInfo,