feat(settings): add a Compact buttons appearance toggle (#1189)

* feat(ui): prototype compact hero and toolbar buttons (Large/Small appearance setting)

* feat(settings): rename action-button size toggle to "Compact buttons"

Promote the hero-button prototype to a real, app-wide setting.

- rename heroButtonSize → buttonSize, data-hero-buttons → data-button-size,
  hero-action-bar/hero-btn-label → compact-action-bar/compact-btn-label
- relabel "Hero buttons" → "Compact buttons" and broaden the description
  (action + toolbar buttons across detail pages and browse views) in all 11 locales
- move the feature CSS out of cover-lightbox.css into its own compact-buttons.css
- add tests: themeStore buttonSize toggle, SelectionToggleButton

* docs(changelog): compact buttons appearance toggle (#1189)

* docs(credits): compact buttons appearance toggle (#1189)

src/App.tsx

@@ -17,6 +17,7 @@ export default function App() {
   useThemeStore(s => s.theme);
   const effectiveTheme = useThemeScheduler();
   const font = useFontStore(s => s.font);
+  const buttonSize = useThemeStore(s => s.buttonSize);
   const installedThemes = useInstalledThemesStore(s => s.themes);
 
   // Document-attribute hooks are shared between both window kinds — each
@@ -81,6 +82,10 @@ export default function App() {
     document.documentElement.setAttribute('data-font', font);
   }, [font]);
 
+  useEffect(() => {
+    document.documentElement.setAttribute('data-button-size', buttonSize);
+  }, [buttonSize]);
+
   // Hide all inline track-preview buttons when the user opts out — single
   // CSS hook (`html[data-track-previews="off"]`) instead of conditional
   // rendering in every tracklist. Per-location toggles use additional