fix(agent): only suppress final reply when message tool sends to same target

A refactoring in commit 132807a introduced a regression where the final
response was silently discarded whenever the message tool was used,
regardless of the target. This restored the original logic from PR #832
that only suppresses the final reply when the message tool sends to the
same (channel, chat_id) as the original message.

Changes:
- message.py: Replace _sent_in_turn: bool with _turn_sends: list[tuple]
  to track actual send targets, add get_turn_sends() method
- loop.py: Check if (msg.channel, msg.chat_id) is in sent_targets before
  suppressing final reply. Also move the "Response to" log after the
  suppress check to avoid misleading logs.
- Add unit tests for the suppress logic

This ensures:
- Email sent via message tool → Feishu still gets confirmation
- Message tool sends to same Feishu chat → No duplicate (suppressed)

nanobot/agent/tools/message.py

@@ -20,7 +20,7 @@ class MessageTool(Tool):
         self._default_channel = default_channel
         self._default_chat_id = default_chat_id
         self._default_message_id = default_message_id
-        self._sent_in_turn: bool = False
+        self._turn_sends: list[tuple[str, str]] = []
 
     def set_context(self, channel: str, chat_id: str, message_id: str | None = None) -> None:
         """Set the current message context."""
@@ -34,7 +34,11 @@ class MessageTool(Tool):
 
     def start_turn(self) -> None:
         """Reset per-turn send tracking."""
-        self._sent_in_turn = False
+        self._turn_sends.clear()
+
+    def get_turn_sends(self) -> list[tuple[str, str]]:
+        """Get (channel, chat_id) targets sent in the current turn."""
+        return list(self._turn_sends)
 
     @property
     def name(self) -> str:
@@ -101,7 +105,7 @@ class MessageTool(Tool):
 
         try:
             await self._send_callback(msg)
-            self._sent_in_turn = True
+            self._turn_sends.append((channel, chat_id))
             media_info = f" with {len(media)} attachments" if media else ""
             return f"Message sent to {channel}:{chat_id}{media_info}"
         except Exception as e: