test(HH-558): complete WebChannel sender display regression matrix (#141)

* chore(agent): baseline — uncommitted work from the local directory

* test(HH-558): cover widget sender display matrix

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Co-authored-by: Rogee <rogee@ipao.vip>

frontend/testdata/visitor_ws_payload.json

@@ -0,0 +1,10 @@
+{
+  "event": "message.created",
+  "data": {
+    "id": 12,
+    "content": "Dashboard reply",
+    "message_type": 1,
+    "conversation_id": 42,
+    "additional_attributes": {}
+  }
+}