fix(issue-50): the monitor labels a row with the server that answered

A `default` scan runs without -L, so the shim answers it from the inherited
HERDR_SESSION_NAME; a create's reconcile --once labelled that server's panes
`default`, and since create adopts only a row of its own server (1e25cf2f
F2), parallel creates in one folder were refused (test_tier4_e2e scenario 4).
The skill-blocks data follows create_session.sh's SystemExit line.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

tests/data/skill_code_blocks.json

@@ -617,7 +617,7 @@
     "other"
    ],
    "passthrough": {
-    "4": "multi-agent-mux-create/scripts/create_session.sh:546"
+    "4": "multi-agent-mux-create/scripts/create_session.sh:550"
    }
   }
  },