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/config/definitions/options-integrations.ts

@@ -258,7 +258,8 @@ export function buildIntegrationConfigOptionRegistry(
       kind: 'enum',
       enumValues: ['headword', 'surface'],
       defaultValue: defaultConfig.ankiConnect.knownWords.matchMode,
-      description: 'Known-word matching strategy for subtitle annotations.',
+      description:
+        'Known-word matching strategy for subtitle annotations. Cache matches always receive known-word highlighting even when POS filters suppress other annotation types.',
     },
     {
       path: 'ankiConnect.knownWords.highlightEnabled',