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/locales/de/settings.ts

@@ -648,6 +648,11 @@ export const settings = {
   sidebarLyricsStyleAppleDesc: 'Aktive Zeile oben mit sanfter Animation.',
   seekbarStyle: 'Seekbar-Stil',
   seekbarStyleDesc: 'Aussehen der Wiedergabe-Seekbar auswählen',
+  buttonSizeTitle: 'Kompakte Buttons',
+  buttonSizeLabel: 'Buttongröße',
+  buttonSizeDesc: 'Verkleinert die Aktions- und Toolbar-Buttons auf Symbole — in Detailseiten und Übersichten.',
+  buttonSize_large: 'Groß',
+  buttonSize_small: 'Klein',
   seekbarTruewave: 'Echte Wellenform',
   seekbarPseudowave: 'Pseudo-Wellenform',
   seekbarLinedot: 'Linie & Punkt',