feat: label source branch deletion security events

frontend/security-center.js

@@ -231,6 +231,7 @@
         passkey_counter_anomaly: 'Passkey counter anomaly',
         device_revoked: 'Device access revoked', all_sessions_revoked: 'All device access revoked',
         issue_closed: 'Issue closed', pull_merged: 'Pull request merged',
+        source_branch_deleted: 'Source branch deleted',
         comment_deleted: 'Comment deleted',
         pull_review_approved: 'Pull request approved',
         pull_review_changes_requested: 'Changes requested', gitea_time_logged: 'Gitea time logged',