feat(overlay): Anki maturity-based known-word highlighting

Color known-word subtitle highlights by Anki card maturity (new,
learning, young, mature) like asbplayer (#171). Notes are classified
server-side with Anki search filters (prop:ivl, is:learn) during the
known-word cache refresh, so no per-card data is fetched. A word's tier
is its most mature matching card/note, with the same reading-aware
matching as boolean known-word lookups.

- known-word cache v4 state persists per-note tiers; lifecycle key only
  gains the maturity field while enabled so existing caches survive
- ankiConnect.knownWords.maturityEnabled + matureThresholdDays (21)
- subtitleStyle.knownWordMaturityColors with catppuccin defaults
- word-maturity-<tier> class rides on word-known so hover/selection
  rules keep applying; falls back to knownWordColor without tier data
- runtime toggle subtitle.annotation.knownWords.maturityEnabled

src/main/runtime/subtitle-tokenization-main-deps.ts

@@ -42,6 +42,12 @@ export function createBuildTokenizerDepsMainHandler(deps: TokenizerMainDeps) {
       deps.recordLookup(hit);
       return hit;
     },
+    ...(deps.getKnownWordTier
+      ? {
+          getKnownWordTier: (text, reading, options) =>
+            deps.getKnownWordTier!(text, reading, options),
+        }
+      : {}),
     getKnownWordMatchMode: () => deps.getKnownWordMatchMode(),
     ...(deps.getKnownWordsEnabled
       ? {