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

changes/remove-dead-code.md

@@ -0,0 +1,5 @@
+type: internal
+area: cleanup
+
+- Removed dead code: the unused launcher Jimaku client (the `SUBMINER_JIMAKU_*` env vars it read were documented but had no effect), the mpv plugin's hover-highlight module (no sender since Overlay 2.0; custom mpv scripts that still send `subminer-hover-token` or `yomipv-hover-token` are now ignored), the never-read `anilist.characterDictionary.refreshTtlHours` / `evictionPolicy` config keys, unused root dependencies (eslint, geist fonts), and a committed draft plan doc.
+- Typecheck now runs with `noUnusedLocals`; removed the unused locals, imports, and the Windows overlay focus-handoff values they fed, which were computed but never used.