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/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',