fix: start system default sync channels by default

Create and restart paths enable IsSystemDefault channels; SyncPage auto-starts after save.

Co-authored-by: Cursor <cursoragent@cursor.com>

platform/internal/logic/applogic/agent_sync_bind.go

@@ -63,7 +63,7 @@ func (l *AgentAdminLogic) ensureAgentSyncBind(acc *agentstore.Account) (*agentst
 	if driver == "" {
 		driver = dbsync.DriverPostgres
 	}
-	ch, err := l.svcCtx.DBSync.Store().EnsureSystemDefaultChannel(dbsync.DefaultChannelOpts{
+	ch, err := l.svcCtx.DBSync.EnsureAndStartSystemDefaultChannel(dbsync.DefaultChannelOpts{
 		TenantID:     acc.TenantID,
 		AgentID:      acc.AgentID,
 		Name:         fmt.Sprintf("默认同步 · %s", acc.Name),