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/preload-settings.test.ts

@@ -21,3 +21,13 @@ test('settings preload exposes Anki lookup helpers', () => {
     assert.match(source, new RegExp(`${method}:`));
   }
 });
+
+test('overlay preload queues subtitle updates until renderer listener registration', () => {
+  const source = fs.readFileSync(path.join(process.cwd(), 'src', 'preload.ts'), 'utf8');
+
+  assert.match(
+    source,
+    /const onSubtitleSetEvent =\s*createQueuedIpcListenerWithPayload<SubtitleData>\(\s*IPC_CHANNELS\.event\.subtitleSet,/,
+  );
+  assert.match(source, /onSubtitle:\s*\(callback:[\s\S]+?onSubtitleSetEvent\(callback\);/);
+});