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/config/definitions/options-subtitle.ts

@@ -181,6 +181,13 @@ export function buildSubtitleConfigOptionRegistry(
       defaultValue: defaultConfig.subtitleSidebar.autoScroll,
       description: 'Auto-scroll the active subtitle cue into view while playback advances.',
     },
+    {
+      path: 'subtitleSidebar.css',
+      kind: 'object',
+      defaultValue: defaultConfig.subtitleSidebar.css,
+      description:
+        'CSS declaration object applied to the subtitle sidebar. Includes color, background-color, and all font properties.',
+    },
     {
       path: 'subtitleSidebar.maxWidth',
       kind: 'number',