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/resolve/subtitle-domains.ts

@@ -521,6 +521,19 @@ export function applySubtitleDomainConfig(context: ResolveContext): void {
       ...(src.subtitleSidebar as ResolvedConfig['subtitleSidebar']),
     };
 
+    const css = asCssDeclarations((src.subtitleSidebar as { css?: unknown }).css);
+    if (css !== undefined) {
+      resolved.subtitleSidebar.css = css;
+    } else if ((src.subtitleSidebar as { css?: unknown }).css !== undefined) {
+      resolved.subtitleSidebar.css = fallback.css;
+      warn(
+        'subtitleSidebar.css',
+        (src.subtitleSidebar as { css?: unknown }).css,
+        resolved.subtitleSidebar.css,
+        'Expected an object whose values are CSS declaration strings.',
+      );
+    }
+
     const enabled = asBoolean((src.subtitleSidebar as { enabled?: unknown }).enabled);
     if (enabled !== undefined) {
       resolved.subtitleSidebar.enabled = enabled;