fix: remove hardcoded assistant acks after system message injection

s08/s09/s10/s11/s_full inject background-results and inbox as user
  messages before LLM calls. The paired hardcoded assistant "Noted..."
  responses were unnecessary — consecutive user messages work fine and
  the fake acks added noise with no functional value.

  Affected: agents/s08, s09, s10, s11, s_full + docs (zh/en/ja s08, s09)

agents/s10_team_protocols.py

@@ -431,10 +431,6 @@ def agent_loop(messages: list):
                 "role": "user",
                 "content": f"<inbox>{json.dumps(inbox, indent=2)}</inbox>",
             })
-            messages.append({
-                "role": "assistant",
-                "content": "Noted inbox messages.",
-            })
         response = client.messages.create(
             model=MODEL,
             system=SYSTEM,