fix(tools): forward thread_id via metadata in _send_via_adapter live path

The live adapter path in _send_via_adapter called adapter.send() without
passing thread_id, while the standalone fallback path correctly forwarded
it. For plugin platforms (google_chat, teams, irc, line) running with the
gateway in-process, this caused every threaded reply to land as a new
top-level message instead of continuing the thread.

Matches the pattern already used by _send_matrix_via_adapter and
_send_feishu: build metadata={"thread_id": thread_id} and pass it through.

tools/send_message_tool.py

@@ -461,7 +461,8 @@ async def _send_via_adapter(
             adapter = None
         if adapter is not None:
             try:
-                result = await adapter.send(chat_id=chat_id, content=chunk)
+                metadata = {"thread_id": thread_id} if thread_id else None
+                result = await adapter.send(chat_id=chat_id, content=chunk, metadata=metadata)
             except asyncio.CancelledError:
                 raise
             except Exception as e: