feat(linux): add WebKitGTK smooth wheel scroll toggle in settings

Persist preference in auth store, sync from App on Linux, and expose a
Tauri command using webkit2gtk to toggle enable-smooth-scrolling at
runtime. Default on to match upstream; users may disable for discrete
GTK-style line steps.

Apply a one-time rehydrate migration so smooth scrolling stays on after
updates even if an older build persisted the wrong default.

src/App.tsx

@@ -139,6 +139,7 @@ function AppShell() {
   const activeServerId = useAuthStore(s => s.activeServerId);
   const setMusicFolders = useAuthStore(s => s.setMusicFolders);
   const useCustomTitlebar = useAuthStore(s => s.useCustomTitlebar);
+  const linuxWebkitKineticScroll = useAuthStore(s => s.linuxWebkitKineticScroll);
   const setEntityRatingSupport = useAuthStore(s => s.setEntityRatingSupport);
   const offlineAlbums = useOfflineStore(s => s.albums);
   const hasOfflineContent = Object.values(offlineAlbums).some(a => a.serverId === serverId);
@@ -151,6 +152,11 @@ function AppShell() {
     invoke('set_window_decorations', { enabled }).catch(() => {});
   }, [useCustomTitlebar, isTilingWm]);
 
+  useEffect(() => {
+    if (!IS_LINUX) return;
+    invoke('set_linux_webkit_smooth_scrolling', { enabled: linuxWebkitKineticScroll }).catch(() => {});
+  }, [linuxWebkitKineticScroll]);
+
   useEffect(() => {
     if (!isLoggedIn || !activeServerId) return;
     const serverAtStart = activeServerId;

src/locales/de.ts

@@ -538,6 +538,8 @@ export const deTranslation = {
     discordRichPresenceDesc: 'Zeigt den aktuell gespielten Titel im Discord-Profil an. Discord muss dafür geöffnet sein.',
     useCustomTitlebar: 'Eigene Titelleiste',
     useCustomTitlebarDesc: 'Ersetzt die System-Titelleiste durch eine eingebaute, die zum App-Theme passt. Deaktivieren, um die native GNOME/GTK-Titelleiste zu verwenden.',
+    linuxWebkitSmoothScroll: 'Sanftes Mausrad (Linux)',
+    linuxWebkitSmoothScrollDesc: 'An: mit Nachlauf. Aus: zeilenweise wie in GTK-Apps.',
     discordAppleCovers: 'Cover über Apple Music für Discord laden',
     discordAppleCoversDesc: 'Sendet Künstler- und Albumname an die Apple-Such-API, um Cover für dein Discord-Profil zu finden. Standardmäßig aus Datenschutzgründen deaktiviert.',
     discordOptions: 'Erweiterte Discord-Optionen',

src/locales/en.ts

@@ -540,6 +540,8 @@ export const enTranslation = {
     discordRichPresenceDesc: 'Show the currently playing track on your Discord profile. Requires Discord to be running.',
     useCustomTitlebar: 'Custom title bar',
     useCustomTitlebarDesc: 'Replace the system title bar with a built-in one that matches the app theme. Disable to use the native GNOME/GTK title bar.',
+    linuxWebkitSmoothScroll: 'Smooth wheel (Linux)',
+    linuxWebkitSmoothScrollDesc: 'On: inertial scroll. Off: line-by-line, GTK-style.',
     discordAppleCovers: 'Fetch covers from Apple Music for Discord',
     discordAppleCoversDesc: 'Sends the artist and album name to Apple\'s search API to find cover art for your Discord profile. Disabled by default for privacy.',
     discordOptions: 'Advanced Discord options',

src/locales/es.ts

@@ -541,6 +541,8 @@ export const esTranslation = {
     discordRichPresenceDesc: 'Muestra la pista actual en tu perfil de Discord. Requiere que Discord esté ejecutándose.',
     useCustomTitlebar: 'Barra de título personalizada',
     useCustomTitlebarDesc: 'Reemplaza la barra de título del sistema con una integrada que coincide con el tema de la app. Desactiva para usar la barra nativa de GNOME/GTK.',
+    linuxWebkitSmoothScroll: 'Rueda suave (Linux)',
+    linuxWebkitSmoothScrollDesc: 'Activado: inercia. Desactivado: pasos por línea (estilo GTK).',
     discordAppleCovers: 'Obtener portadas de Apple Music para Discord',
     discordAppleCoversDesc: 'Envía el artista y nombre del álbum a la API de búsqueda de Apple para encontrar portadas para tu perfil de Discord. Desactivado por defecto por privacidad.',
     discordOptions: 'Opciones avanzadas de Discord',

src/locales/fr.ts

@@ -534,6 +534,8 @@ export const frTranslation = {
     showTrayIconDesc: 'Affiche l\'icône Psysonic dans la zone de notification / barre des menus.',
     minimizeToTray: 'Réduire dans la barre système',
     minimizeToTrayDesc: 'Lors de la fermeture, Psysonic continue de fonctionner dans la barre système au lieu de se fermer.',
+    linuxWebkitSmoothScroll: 'Molette fluide (Linux)',
+    linuxWebkitSmoothScrollDesc: 'Activé : inertie. Désactivé : pas à la ligne, style GTK.',
     discordRichPresence: 'Discord Rich Presence',
     discordRichPresenceDesc: 'Affiche le titre en cours de lecture sur votre profil Discord. Discord doit être ouvert.',
     discordAppleCovers: 'Récupérer les pochettes via Apple Music pour Discord',

src/locales/nb.ts

@@ -533,6 +533,8 @@ export const nbTranslation = {
     showArtistImagesDesc: 'Last inn og vis artistbilder i artistoversikten. Denne er deaktivert som standard, for å redusere disk-I/O og nettverksbelastningen på store biblioteker.',
     minimizeToTray: 'Minimer til oppgavelinjen',
     minimizeToTrayDesc: 'Når vinduet lukkes, vil Psysonic bli kjørende i oppgavelinjen fremfor å bli avsluttet.',
+    linuxWebkitSmoothScroll: 'Mykt musehjul (Linux)',
+    linuxWebkitSmoothScrollDesc: 'På: treg rull med etterslep. Av: trinnvis som i GTK.',
     discordRichPresence: 'Discord Rich Presence',
     discordRichPresenceDesc: 'Vis sporet som spilles i din Discord-profil. Krever at Discord kjører.',
     discordAppleCovers: 'Hent covere fra Apple Music til Discord',

src/locales/nl.ts

@@ -533,6 +533,8 @@ export const nlTranslation = {
     showTrayIconDesc: 'Toont het Psysonic-pictogram in het systeemvak / de menubalk.',
     minimizeToTray: 'Minimaliseren naar systeemvak',
     minimizeToTrayDesc: 'Bij het sluiten van het venster blijft Psysonic actief in het systeemvak in plaats van af te sluiten.',
+    linuxWebkitSmoothScroll: 'Vloeiend muiswiel (Linux)',
+    linuxWebkitSmoothScrollDesc: 'Aan: traag naloop. Uit: regel voor regel, GTK-stijl.',
     discordRichPresence: 'Discord Rich Presence',
     discordRichPresenceDesc: 'Toont het huidige nummer op je Discord-profiel. Discord moet daarvoor geopend zijn.',
     discordAppleCovers: 'Hoezen ophalen via Apple Music voor Discord',

src/locales/ru.ts

@@ -555,6 +555,8 @@ export const ruTranslation = {
     useCustomTitlebar: 'Своя строка заголовка',
     useCustomTitlebarDesc:
       'Заменить системную строку заголовка встроенной, в стиле темы приложения. Отключите, чтобы использовать родную строку GNOME/GTK и т.д.',
+    linuxWebkitSmoothScroll: 'Плавное колесо (Linux)',
+    linuxWebkitSmoothScrollDesc: 'Вкл — инерция. Выкл — по шагам, как в GTK.',
     discordRichPresence: 'Статус в Discord',
     discordRichPresenceDesc:
       'Показывать текущий трек в профиле и статусе Discord. Нужен запущенный клиент Discord.',

src/locales/zh.ts

@@ -529,6 +529,8 @@ export const zhTranslation = {
     showTrayIconDesc: '在系统通知区域 / 菜单栏显示 Psysonic 图标。',
     minimizeToTray: '最小化到托盘',
     minimizeToTrayDesc: '关闭窗口时，Psysonic 将继续在系统托盘中运行，而不是退出。',
+    linuxWebkitSmoothScroll: '滚轮平滑（Linux）',
+    linuxWebkitSmoothScrollDesc: '开：惯性滚动。关：逐行，类似 GTK。',
     discordRichPresence: 'Discord Rich Presence',
     discordRichPresenceDesc: '在 Discord 个人资料上显示当前播放的曲目。需要 Discord 处于运行状态。',
     discordAppleCovers: '通过 Apple Music 为 Discord 获取封面',

src/pages/Settings.tsx

@@ -1136,6 +1136,25 @@ export default function Settings() {
                   </div>
                 </>
               )}
+              {IS_LINUX && (
+                <>
+                  <div className="settings-section-divider" />
+                  <div className="settings-toggle-row">
+                    <div>
+                      <div style={{ fontWeight: 500 }}>{t('settings.linuxWebkitSmoothScroll')}</div>
+                      <div style={{ fontSize: 12, color: 'var(--text-muted)' }}>{t('settings.linuxWebkitSmoothScrollDesc')}</div>
+                    </div>
+                    <label className="toggle-switch" aria-label={t('settings.linuxWebkitSmoothScroll')}>
+                      <input
+                        type="checkbox"
+                        checked={auth.linuxWebkitKineticScroll}
+                        onChange={e => auth.setLinuxWebkitKineticScroll(e.target.checked)}
+                      />
+                      <span className="toggle-track" />
+                    </label>
+                  </div>
+                </>
+              )}
               <div className="settings-section-divider" />
               <div className="settings-toggle-row">
                 <div>

src/store/authStore.ts

@@ -65,6 +65,8 @@ interface AuthState {
   discordTemplateState: string;
   discordTemplateLargeText: string;
   useCustomTitlebar: boolean;
+  /** Linux WebKitGTK: smooth wheel on when true; off only after explicit opt-out in Settings. */
+  linuxWebkitKineticScroll: boolean;
   nowPlayingEnabled: boolean;
   lyricsServerFirst: boolean;
   enableNeteaselyrics: boolean;
@@ -209,6 +211,7 @@ interface AuthState {
   setDiscordTemplateState: (v: string) => void;
   setDiscordTemplateLargeText: (v: string) => void;
   setUseCustomTitlebar: (v: boolean) => void;
+  setLinuxWebkitKineticScroll: (v: boolean) => void;
   setNowPlayingEnabled: (v: boolean) => void;
   setLyricsServerFirst: (v: boolean) => void;
   setEnableNeteaselyrics: (v: boolean) => void;
@@ -314,6 +317,7 @@ export const useAuthStore = create<AuthState>()(
       discordTemplateState: '{album}',
       discordTemplateLargeText: '{album}',
       useCustomTitlebar: false,
+      linuxWebkitKineticScroll: true,
       nowPlayingEnabled: false,
       lyricsServerFirst: true,
       enableNeteaselyrics: false,
@@ -443,6 +447,7 @@ export const useAuthStore = create<AuthState>()(
       setDiscordTemplateState: (v) => set({ discordTemplateState: v }),
       setDiscordTemplateLargeText: (v) => set({ discordTemplateLargeText: v }),
       setUseCustomTitlebar: (v) => set({ useCustomTitlebar: v }),
+      setLinuxWebkitKineticScroll: (v) => set({ linuxWebkitKineticScroll: v }),
       setNowPlayingEnabled: (v) => set({ nowPlayingEnabled: v }),
       setLyricsServerFirst: (v: boolean) => set({ lyricsServerFirst: v }),
       setEnableNeteaselyrics: (v: boolean) => set({ enableNeteaselyrics: v }),
@@ -630,6 +635,18 @@ export const useAuthStore = create<AuthState>()(
           }
         } catch { /* ignore */ }
 
+        // One-time: older builds could persist smooth=false as the default. Force smooth on once
+        // so updates do not leave users on discrete scrolling; after this flag exists, only an
+        // explicit toggle in Settings may turn it off (persisted in psysonic-auth).
+        const wheelSmoothMigrationKey = 'psysonic-linux-webkit-smooth-v1';
+        let wheelSmoothOneTime: { linuxWebkitKineticScroll?: boolean } = {};
+        try {
+          if (!localStorage.getItem(wheelSmoothMigrationKey)) {
+            wheelSmoothOneTime = { linuxWebkitKineticScroll: true };
+            localStorage.setItem(wheelSmoothMigrationKey, '1');
+          }
+        } catch { /* ignore */ }
+
         useAuthStore.setState({
           mixMinRatingSong: clampMixFilterMinStars(state.mixMinRatingSong as number),
           mixMinRatingAlbum: clampMixFilterMinStars(state.mixMinRatingAlbum as number),
@@ -639,6 +656,7 @@ export const useAuthStore = create<AuthState>()(
           ),
           ...conflictingLegacyState,
           ...lyricsSourcesMigrated,
+          ...wheelSmoothOneTime,
         });
       },
     }