fix(node): never sweep a node's inbounds before their first adoption

Adding a node imports nothing; its pre-existing inbounds only become
central rows on the first clean traffic-sync tick. But any save of the
node (switching sync mode, picking tags after "Load inbounds from
node") marks it config-dirty, and the next tick then ran ReconcileNode
before that first adoption: with zero central rows the delete sweep saw
every remote tag as undesired and destroyed the node's real inbounds -
in "all" mode all of them - disconnecting live clients with no
confirmation, and the master then reported "record not found".

Track the first completed clean sync in nodes.inbounds_adopted_at and
skip the sweep (pushes still run) until it is set, so "absent locally"
can no longer be conflated with "deleted on the master". A node that
has synced before still sweeps normally, including the offline
last-inbound-deleted case. Existing nodes are seeded as adopted on
upgrade to keep their behavior unchanged.

Closes #5898

internal/web/service/node.go

@@ -771,6 +771,15 @@ func (s *NodeService) ClearNodeDirty(id int, dirtyAt int64) error {
 		Update("config_dirty", false).Error
 }
 
+func (s *NodeService) MarkNodeInboundsAdopted(id int) error {
+	if id <= 0 {
+		return nil
+	}
+	return database.GetDB().Model(model.Node{}).
+		Where("id = ? AND inbounds_adopted_at = 0", id).
+		Update("inbounds_adopted_at", time.Now().Unix()).Error
+}
+
 func (s *NodeService) NodeSyncState(id int) (enabled bool, status string, dirty bool, dirtyAt int64, err error) {
 	if id <= 0 {
 		return false, "", false, 0, errors.New("invalid node id")