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/store/deviceSyncJobStore.ts

@@ -11,6 +11,7 @@ export interface DeviceSyncJobState {
   startSync: (jobId: string, total: number) => void;
   updateProgress: (done: number, skipped: number, failed: number) => void;
   complete: (done: number, skipped: number, failed: number) => void;
+  cancel: () => void;
   reset: () => void;
 }
 
@@ -31,6 +32,9 @@ export const useDeviceSyncJobStore = create<DeviceSyncJobState>()((set) => ({
   complete: (done, skipped, failed) =>
     set({ done, skipped, failed, status: 'done' }),
 
+  cancel: () =>
+    set({ status: 'cancelled' }),
+
   reset: () =>
     set({ jobId: null, total: 0, done: 0, skipped: 0, failed: 0, status: 'idle' }),
 }));

src/store/fontStore.ts

@@ -1,7 +1,7 @@
 import { create } from 'zustand';
 import { persist } from 'zustand/middleware';
 
-export type FontId = 'inter' | 'outfit' | 'dm-sans' | 'nunito' | 'rubik' | 'space-grotesk' | 'figtree' | 'manrope' | 'plus-jakarta-sans' | 'lexend';
+export type FontId = 'inter' | 'outfit' | 'dm-sans' | 'nunito' | 'rubik' | 'space-grotesk' | 'figtree' | 'manrope' | 'plus-jakarta-sans' | 'lexend' | 'geist' | 'jetbrains-mono';
 
 interface FontState {
   font: FontId;