feat(client): add sync queue management for offline sync

Implement SyncQueue class to manage pending changes for offline sync:
- Track unsynced decks, cards, and review logs from IndexedDB
- Manage sync status (idle, syncing, error) with listener support
- Persist last sync version and timestamp to localStorage
- Provide methods to mark items as synced after push
- Apply pulled changes from server to local database

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/client/sync/index.ts b/src/client/sync/index.ts
new file mode 100644
index 0000000..6f75a29
--- /dev/null
+++ b/src/client/sync/index.ts
@@ -0,0 +1,9 @@
+export {
+	SyncQueue,
+	SyncStatus,
+	syncQueue,
+	type PendingChanges,
+	type SyncQueueListener,
+	type SyncQueueState,
+	type SyncStatusType,
+} from "./queue";