feat(teams): add task approval workflow with approve/reject actions

Tasks can be created with require_approval flag, starting in
pending_approval status. Users approve/reject via tool actions or
WS methods. Approval respects blocked_by dependencies — tasks with
unresolved blockers transition to blocked instead of pending.
Delegate agents are restricted from approving/rejecting.

pkg/protocol/methods.go

@@ -107,6 +107,8 @@ const (
 	MethodTeamsGet      = "teams.get"
 	MethodTeamsDelete   = "teams.delete"
 	MethodTeamsTaskList      = "teams.tasks.list"
+	MethodTeamsTaskApprove   = "teams.tasks.approve"
+	MethodTeamsTaskReject    = "teams.tasks.reject"
 	MethodTeamsMembersAdd    = "teams.members.add"
 	MethodTeamsMembersRemove = "teams.members.remove"
 	MethodTeamsUpdate        = "teams.update"