refactor: remove dead code and enable noUnusedLocals (#292)

* refactor: remove dead code and enable noUnusedLocals

- delete launcher/jimaku.ts and the launcher Args/config jimaku* fields
  that only fed it (the SUBMINER_JIMAKU_* env vars had no effect)
- delete plugin/subminer/hover.lua; nothing has sent subminer-hover-token
  since Overlay 2.0
- drop never-read anilist.characterDictionary.refreshTtlHours and
  evictionPolicy (still hidden in the settings UI for old configs)
- drop unused root deps: eslint, @fontsource-variable/geist{,-mono}
  (stats/ declares its own)
- delete the committed draft renderer-performance plan doc
- turn on noUnusedLocals for typecheck and remove what it surfaced,
  including Windows focus-handoff values computed but never consumed

* docs(changes): add docs fragment and note retired hover messages

src/core/services/anilist/anilist-updater.ts

@@ -87,20 +87,6 @@ export interface GuessAnilistMediaInfoDeps {
   runGuessit: (target: string) => Promise<string>;
 }
 
-function firstString(value: unknown): string | null {
-  if (typeof value === 'string') {
-    const trimmed = value.trim();
-    return trimmed.length > 0 ? trimmed : null;
-  }
-  if (Array.isArray(value)) {
-    for (const item of value) {
-      const candidate = firstString(item);
-      if (candidate) return candidate;
-    }
-  }
-  return null;
-}
-
 function normalizeGuessitTitlePart(value: string): string {
   return value.replace(/[._]+/g, ' ').replace(/-/g, ' ').replace(/\s+/g, ' ').trim();
 }