feat(web-sync): add background sync worker and retry strategy

apps/web/src/services/local-db.ts

@@ -47,10 +47,33 @@ export type LocalTaskDraftRecord = {
   updatedAt: number;
 };
 
+export type LocalSyncStateRecord = {
+  userId: string;
+  cursor: string | null;
+  lastSyncedAt: number | null;
+  updatedAt: number;
+};
+
+export type LocalSyncInboxRecord = {
+  opId: string;
+  userId: string;
+  entityId: string;
+  entityType: SyncEntityType;
+  action: SyncActionType;
+  payload: string | null;
+  clientTs: number;
+  deviceId: string;
+  serverTs: number;
+  receivedAt: number;
+  appliedAt: number | null;
+};
+
 class TodoLocalDb extends Dexie {
   declare tasks: Table<LocalTaskRecord, string>;
   declare opLogs: Table<LocalOpLogRecord, string>;
   declare taskDrafts: Table<LocalTaskDraftRecord, string>;
+  declare syncStates: Table<LocalSyncStateRecord, string>;
+  declare syncInbox: Table<LocalSyncInboxRecord, string>;
 
   constructor() {
     super("todolist-web-db");
@@ -66,9 +89,19 @@ class TodoLocalDb extends Dexie {
       task_drafts: "&taskId,userId,updatedAt"
     });
 
+    this.version(3).stores({
+      tasks: "&id,userId,status,priority,ddlAt,updatedAt,deletedAt",
+      op_logs: "&opId,entityId,entityType,action,clientTs,syncedAt",
+      task_drafts: "&taskId,userId,updatedAt",
+      sync_states: "&userId,updatedAt,lastSyncedAt",
+      sync_inbox: "&opId,userId,entityId,serverTs,appliedAt"
+    });
+
     this.tasks = this.table("tasks");
     this.opLogs = this.table("op_logs");
     this.taskDrafts = this.table("task_drafts");
+    this.syncStates = this.table("sync_states");
+    this.syncInbox = this.table("sync_inbox");
   }
 }