feat(tray): show now-playing track in tray + i18n menu labels (#395)

* feat(tray): show now-playing track in tray icon tooltip

Mirrors the current track to the tray tooltip ("Artist – Title") on every
play/pause/track change, falling back to "Psysonic" when nothing is playing.
The cached value survives tray hide/show via a new TrayTooltip state, and
is truncated to 127 chars for Windows NOTIFYICONDATA.szTip.

Closes #383


* feat(tray): linux fallback — disabled menu item shows now-playing track

AppIndicator on Linux has no hover-tooltip API, so the tooltip command was
a silent no-op there. Adds a disabled menu entry at the top of the tray
right-click menu that mirrors the same text. Updated in lockstep with the
Win/macOS tooltip via set_tray_tooltip.

* i18n(tray): localize tray menu labels

Adds a `tray` namespace in all 8 locales (en/de/fr/nl/zh/nb/ru/es) for
Play/Pause, Next/Previous, Show/Hide, Exit, and the Linux-only
"Nothing playing" placeholder.

Rust side: TrayMenuLabels state holds the cached translations and
TrayMenuItems holds the live MenuItem handles. New set_tray_menu_labels
command pushes new strings + applies them via set_text without rebuilding
the tray icon.

Frontend pushes the labels on mount and on every i18n.on('languageChanged').

src/locales/de.ts

@@ -1730,4 +1730,12 @@ export const deTranslation = {
     exitEndedBody: '„{{name}}" ist zu Ende. Hoffentlich war\'s schön.',
     exitOk: 'OK',
   },
+  tray: {
+    playPause: 'Wiedergabe / Pause',
+    nextTrack: 'Nächster Titel',
+    previousTrack: 'Vorheriger Titel',
+    showHide: 'Anzeigen / Verbergen',
+    exitPsysonic: 'Psysonic beenden',
+    nothingPlaying: 'Nichts wird abgespielt',
+  },
 };

src/locales/en.ts

@@ -1737,4 +1737,12 @@ export const enTranslation = {
     exitEndedBody: '"{{name}}" has ended. Hope you had fun.',
     exitOk: 'OK',
   },
+  tray: {
+    playPause: 'Play / Pause',
+    nextTrack: 'Next Track',
+    previousTrack: 'Previous Track',
+    showHide: 'Show / Hide',
+    exitPsysonic: 'Exit Psysonic',
+    nothingPlaying: 'Nothing playing',
+  },
 };

src/locales/es.ts

@@ -1717,4 +1717,12 @@ export const esTranslation = {
     exitEndedBody: '"{{name}}" ha terminado. Espero que te hayas divertido.',
     exitOk: 'OK',
   },
+  tray: {
+    playPause: 'Reproducir / Pausa',
+    nextTrack: 'Pista siguiente',
+    previousTrack: 'Pista anterior',
+    showHide: 'Mostrar / Ocultar',
+    exitPsysonic: 'Salir de Psysonic',
+    nothingPlaying: 'Nada en reproducción',
+  },
 };

src/locales/fr.ts

@@ -1712,4 +1712,12 @@ export const frTranslation = {
     exitEndedBody: '« {{name}} » est terminée. J\'espère que tu t\'es bien amusé.',
     exitOk: 'OK',
   },
+  tray: {
+    playPause: 'Lecture / Pause',
+    nextTrack: 'Piste suivante',
+    previousTrack: 'Piste précédente',
+    showHide: 'Afficher / Masquer',
+    exitPsysonic: 'Quitter Psysonic',
+    nothingPlaying: 'Aucune lecture',
+  },
 };

src/locales/nb.ts

@@ -1711,4 +1711,12 @@ export const nbTranslation = {
     exitEndedBody: '"{{name}}" er avsluttet. Håper du hadde det gøy.',
     exitOk: 'OK',
   },
+  tray: {
+    playPause: 'Spill / Pause',
+    nextTrack: 'Neste spor',
+    previousTrack: 'Forrige spor',
+    showHide: 'Vis / Skjul',
+    exitPsysonic: 'Avslutt Psysonic',
+    nothingPlaying: 'Ingenting spilles',
+  },
 };

src/locales/nl.ts

@@ -1711,4 +1711,12 @@ export const nlTranslation = {
     exitEndedBody: '"{{name}}" is beëindigd. Hopelijk had je plezier.',
     exitOk: 'OK',
   },
+  tray: {
+    playPause: 'Afspelen / Pauzeren',
+    nextTrack: 'Volgende nummer',
+    previousTrack: 'Vorige nummer',
+    showHide: 'Tonen / Verbergen',
+    exitPsysonic: 'Psysonic afsluiten',
+    nothingPlaying: 'Niets wordt afgespeeld',
+  },
 };

src/locales/ru.ts

@@ -1798,4 +1798,12 @@ export const ruTranslation = {
     exitEndedBody: '«{{name}}» завершена. Надеюсь, тебе понравилось.',
     exitOk: 'ОК',
   },
+  tray: {
+    playPause: 'Воспроизвести / Пауза',
+    nextTrack: 'Следующий трек',
+    previousTrack: 'Предыдущий трек',
+    showHide: 'Показать / Скрыть',
+    exitPsysonic: 'Закрыть Psysonic',
+    nothingPlaying: 'Ничего не воспроизводится',
+  },
 };

src/locales/zh.ts

@@ -1704,4 +1704,12 @@ export const zhTranslation = {
     exitEndedBody: '"{{name}}"已结束。希望你玩得开心。',
     exitOk: '好的',
   },
+  tray: {
+    playPause: '播放 / 暂停',
+    nextTrack: '下一首',
+    previousTrack: '上一首',
+    showHide: '显示 / 隐藏',
+    exitPsysonic: '退出 Psysonic',
+    nothingPlaying: '当前没有播放',
+  },
 };