feat(device-sync): manifest, cancel, font picker + sync status fix

- Write psysonic-sync.json to device after sync/deletions; auto-import
  on folder select when localStorage is empty (cross-platform handoff)
- Add cancel button during active sync: AtomicBool flag per job,
  tasks bail after acquiring semaphore, cancelled state in UI
- Fix sync status staying "pending": normalize template path separators
  to OS separator (Windows: '/' → '\') so compute_sync_paths and
  list_device_dir_files produce matching strings for Set comparison
- Add Geist and JetBrains Mono as variable fonts; font picker collapsible
- Fix device mount detection on Windows: removable drive letters (E:\)
  were incorrectly skipped alongside system roots; strip \?\ prefix
  from canonicalized paths before mount-point comparison

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/de.ts

@@ -1085,6 +1085,7 @@ export const deTranslation = {
     deleteFromDevice: 'Vom Gerät löschen ({{count}})',
     confirmDelete: '{{count}} Eintrag/Einträge vom Gerät löschen: {{names}}?',
     deleteComplete: '{{count}} Eintrag/Einträge vom Gerät entfernt.',
+    manifestImported: '{{count}} Quelle(n) aus Geräte-Manifest importiert.',
     selectedSources: 'Ausgewählte Quellen',
     noSourcesSelected: 'Keine Quellen ausgewählt. Klicke auf Einträge im Browser um sie hinzuzufügen.',
     clearAll: 'Alle entfernen',
@@ -1104,6 +1105,8 @@ export const deTranslation = {
     fetchError: 'Fehler beim Laden der Tracks vom Server.',
     syncComplete: 'Übertragung abgeschlossen.',
     dismiss: 'Schließen',
+    cancelSync: 'Abbrechen',
+    syncCancelled: 'Sync abgebrochen ({{done}} / {{total}} übertragen).',
     colStatus: 'Status',
     statusSynced: 'Synchronisiert',
     statusPending: 'Ausstehend',

src/locales/en.ts

@@ -1088,6 +1088,7 @@ export const enTranslation = {
     deleteFromDevice: 'Mark for deletion ({{count}})',
     confirmDelete: 'Delete {{count}} item(s) from the device: {{names}}?',
     deleteComplete: '{{count}} item(s) removed from device.',
+    manifestImported: 'Imported {{count}} source(s) from device manifest.',
     selectedSources: 'Selected Sources',
     noSourcesSelected: 'No sources selected. Click items in the browser to add them.',
     clearAll: 'Clear all',
@@ -1107,6 +1108,8 @@ export const enTranslation = {
     fetchError: 'Failed to fetch tracks from server.',
     syncComplete: 'Sync complete.',
     dismiss: 'Dismiss',
+    cancelSync: 'Cancel',
+    syncCancelled: 'Sync cancelled ({{done}} / {{total}} transferred).',
     statusSynced: 'Synced',
     statusPending: 'Pending',
     statusDeletion: 'Deletion',

src/locales/es.ts

@@ -1103,6 +1103,8 @@ export const esTranslation = {
     fetchError: 'Error al obtener pistas del servidor.',
     syncComplete: 'Sincronización completada.',
     dismiss: 'Cerrar',
+    cancelSync: 'Cancelar',
+    syncCancelled: 'Sincronización cancelada ({{done}} / {{total}} transferidos).',
     colName: 'Nombre',
     colType: 'Tipo',
     colStatus: 'Estado',
@@ -1112,6 +1114,7 @@ export const esTranslation = {
     deleteFromDevice: 'Marcar para eliminar ({{count}})',
     confirmDelete: '¿Eliminar {{count}} elemento(s) del dispositivo: {{names}}?',
     deleteComplete: '{{count}} elemento(s) eliminado(s) del dispositivo.',
+    manifestImported: '{{count}} fuente(s) importada(s) desde el manifiesto del dispositivo.',
     statusSynced: 'Sincronizado',
     statusPending: 'Pendiente',
     statusDeletion: 'Eliminación',

src/locales/fr.ts

@@ -1098,6 +1098,8 @@ export const frTranslation = {
     fetchError: 'Échec du chargement des pistes depuis le serveur.',
     syncComplete: 'Synchronisation terminée.',
     dismiss: 'Fermer',
+    cancelSync: 'Annuler',
+    syncCancelled: 'Synchronisation annulée ({{done}} / {{total}} transférés).',
     colName: 'Nom',
     colType: 'Type',
     colStatus: 'Statut',
@@ -1107,6 +1109,7 @@ export const frTranslation = {
     deleteFromDevice: 'Marquer pour suppression ({{count}})',
     confirmDelete: 'Supprimer {{count}} élément(s) du périphérique : {{names}} ?',
     deleteComplete: '{{count}} élément(s) supprimé(s) du périphérique.',
+    manifestImported: '{{count}} source(s) importée(s) depuis le manifeste du périphérique.',
     statusSynced: 'Synchronisé',
     statusPending: 'En attente',
     statusDeletion: 'Suppression',

src/locales/nb.ts

@@ -1097,6 +1097,8 @@ export const nbTranslation = {
     fetchError: 'Kunne ikke hente spor fra serveren.',
     syncComplete: 'Synkronisering fullført.',
     dismiss: 'Lukk',
+    cancelSync: 'Avbryt',
+    syncCancelled: 'Synkronisering avbrutt ({{done}} / {{total}} overført).',
     colName: 'Navn',
     colType: 'Type',
     colStatus: 'Status',
@@ -1106,6 +1108,7 @@ export const nbTranslation = {
     deleteFromDevice: 'Merk for sletting ({{count}})',
     confirmDelete: 'Slette {{count}} element(er) fra enheten: {{names}}?',
     deleteComplete: '{{count}} element(er) fjernet fra enheten.',
+    manifestImported: '{{count}} kilde(r) importert fra enhetsmanifest.',
     statusSynced: 'Synkronisert',
     statusPending: 'Venter',
     statusDeletion: 'Sletting',

src/locales/nl.ts

@@ -1097,6 +1097,8 @@ export const nlTranslation = {
     fetchError: 'Ophalen van nummers van de server mislukt.',
     syncComplete: 'Synchronisatie voltooid.',
     dismiss: 'Sluiten',
+    cancelSync: 'Annuleren',
+    syncCancelled: 'Synchronisatie geannuleerd ({{done}} / {{total}} overgebracht).',
     colName: 'Naam',
     colType: 'Type',
     colStatus: 'Status',
@@ -1106,6 +1108,7 @@ export const nlTranslation = {
     deleteFromDevice: 'Markeren voor verwijdering ({{count}})',
     confirmDelete: '{{count}} item(s) van het apparaat verwijderen: {{names}}?',
     deleteComplete: '{{count}} item(s) van het apparaat verwijderd.',
+    manifestImported: '{{count}} bron(nen) geïmporteerd uit apparaatmanifest.',
     statusSynced: 'Gesynchroniseerd',
     statusPending: 'In behandeling',
     statusDeletion: 'Verwijdering',

src/locales/ru.ts

@@ -1156,6 +1156,8 @@ export const ruTranslation = {
     fetchError: 'Ошибка загрузки треков с сервера.',
     syncComplete: 'Синхронизация завершена.',
     dismiss: 'Закрыть',
+    cancelSync: 'Отмена',
+    syncCancelled: 'Синхронизация отменена ({{done}} / {{total}} перенесено).',
     colName: 'Название',
     colType: 'Тип',
     colStatus: 'Статус',
@@ -1165,6 +1167,7 @@ export const ruTranslation = {
     deleteFromDevice: 'Пометить для удаления ({{count}})',
     confirmDelete: 'Удалить {{count}} запись(ей) с устройства: {{names}}?',
     deleteComplete: '{{count}} запись(ей) удалено с устройства.',
+    manifestImported: 'Импортировано {{count}} источник(ов) из манифеста устройства.',
     statusSynced: 'Синхронизировано',
     statusPending: 'Ожидает',
     statusDeletion: 'Удаление',

src/locales/zh.ts

@@ -1091,6 +1091,8 @@ export const zhTranslation = {
     fetchError: '从服务器加载曲目失败。',
     syncComplete: '同步完成。',
     dismiss: '关闭',
+    cancelSync: '取消',
+    syncCancelled: '同步已取消（已传输 {{done}} / {{total}}）。',
     colName: '名称',
     colType: '类型',
     colStatus: '状态',
@@ -1100,6 +1102,7 @@ export const zhTranslation = {
     deleteFromDevice: '标记为删除（{{count}}）',
     confirmDelete: '从设备删除 {{count}} 个项目：{{names}}？',
     deleteComplete: '已从设备删除 {{count}} 个项目。',
+    manifestImported: '已从设备清单导入 {{count}} 个来源。',
     statusSynced: '已同步',
     statusPending: '待处理',
     statusDeletion: '删除中',