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/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',