feat(mini-player): user-bindable keyboard shortcut to toggle mini player

Adds an 'open-mini-player' entry to the in-app keybindings (Settings →
Shortcuts), default unbound. Pressing the chord from the main window
opens the mini and minimises main; pressing it from the mini hides the
mini and restores main — both paths invoke open_mini_player which
already handles the toggle.

The mini window has its own keydown listener (same pattern as Space /
arrows for play/skip) that reads the binding from useKeybindingsStore.
Binding changes in main propagate to an open mini through the existing
storage-event sync (now also covers psysonic_keybindings) so the user
doesn't need to restart the mini after rebinding.

Localized in all 8 supported locales.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/App.tsx

@@ -812,6 +812,9 @@ function TauriEventBridge() {
           win.isFullscreen().then(fs => win.setFullscreen(!fs));
           break;
         }
+        case 'open-mini-player':
+          invoke('open_mini_player').catch(() => {});
+          break;
       }
     };
     window.addEventListener('keydown', onKey);
@@ -983,6 +986,7 @@ export default function App() {
       if (!e.key) return;
       if (e.key === 'psysonic_theme') useThemeStore.persist.rehydrate();
       else if (e.key === 'psysonic_font') useFontStore.persist.rehydrate();
+      else if (e.key === 'psysonic_keybindings') useKeybindingsStore.persist.rehydrate();
       else if (e.key === 'psysonic_language' && e.newValue) {
         import('./i18n').then(m => m.default.changeLanguage(e.newValue!));
       }