ci(jenkins): restore branch discovery on titan-iac-quality-gate

The titan-iac-quality-gate multibranch job's git branch source was
defined without a discovery trait, so JCasC created it with empty
traits and it indexed zero branches — no PR ever built, no status
check was ever reported, and auto-merge could never fire. Add
traits { gitBranchDiscovery() } to match every working multibranch
job (e.g. hermes-code-demo-branches).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/jenkins/configmap-jcasc.yaml

@@ -679,6 +679,9 @@ data:
                     id('titan-iac-quality-gate')
                     remote('https://scm.bstein.dev/atlas/titan-iac.git')
                     credentialsId('gitea-pat')
+                    traits {
+                      gitBranchDiscovery()
+                    }
                   }
                 }
               }