feat(tokenizer): refine Yomitan grouping and parser tooling

- map segmented Yomitan lines into single logical tokens and improve candidate selection heuristics

- limit frequency lookup to selected token text with POS-based exclusions and add debug logging hook

- add standalone Yomitan parser test script, deterministic utility-script shutdown, and docs/backlog updates

src/main.ts

@@ -911,6 +911,7 @@ async function tokenizeSubtitle(text: string): Promise<SubtitleData> {
       getFrequencyDictionaryEnabled: () =>
         getResolvedConfig().subtitleStyle.frequencyDictionary.enabled,
       getFrequencyRank: (text) => appState.frequencyRankLookup(text),
+      getYomitanGroupDebugEnabled: () => appState.overlayDebugVisualizationEnabled,
       getMecabTokenizer: () => appState.mecabTokenizer,
     }),
   );