feat(config): unify mpv plugin options under main config and add CSS/Ani

- Replace subminer.conf plugin config with mpv.* fields in config.jsonc
- Add socketPath, backend, autoStartSubMiner, pauseUntilOverlayReady, aniskipEnabled/buttonKey, subminerBinaryPath to mpv config
- Add subtitleSidebar.css field; migrate legacy sidebar appearance fields
- Add paintOrder and WebkitTextStroke to subtitle style options
- Update default subtitle/sidebar fontFamily to CJK-first stack
- Fix overlay visible state surviving mpv y-r restart
- Fix live config saves applying subtitle CSS immediately to open overlays
- Migrate legacy primary/secondary subtitle appearance into subtitleStyle.css on load
- Switch AniSkip button key setting to click-to-learn key capture

src/settings/settings-controls.ts

@@ -153,6 +153,10 @@ export function renderControl(
     return renderKeyboardInput(context, field, 'code');
   }
 
+  if (field.control === 'mpv-key') {
+    return renderKeyboardInput(context, field, 'mpv-key');
+  }
+
   if (field.control === 'known-words-decks') {
     return renderKnownWordsDecksInput(context, field);
   }