fix(iam): enforce admin credential authorization boundaries

Honor self-service authorization denials, prevent session-limited credential delegation and updates, and protect root credential mutations under built-in IAM. Preserve empty-policy inheritance and damaged-account cleanup, normalize new service policy claims at issuance, and add signed Admin API and LDAP regressions.

Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/iam-peer-reload_test.go

@@ -24,6 +24,8 @@ func TestIAMPeerDeleteNotificationReloadsCommittedState(t *testing.T) {
 			resetTestGlobals()
 			ctx, cancel := context.WithCancel(context.Background())
 			defer cancel()
+			// Both caches use object storage, independent of earlier etcd suites.
+			globalEtcdClient = nil
 			obj, disk, err := prepareFS(ctx)
 			if err != nil {
 				t.Fatal(err)