Don't send outbound mentions for direct chats

because KT doesn't allow them, and errors when the bridge sends them

matrix_appservice_kakaotalk/formatter/from_matrix.py

@@ -154,7 +154,11 @@ async def matrix_to_kakaotalk(
         )
     else:
         reply_to = None
-    if content.get("format", None) == Format.HTML and content["formatted_body"] and content.msgtype.is_text:
+    if (
+        content.get("format", None) == Format.HTML and content["formatted_body"] and 
+        content.msgtype.is_text and
+        not portal.is_direct
+    ):
         parsed = await ToKakaoTalkParser().parse(utf16_surrogate.add(content["formatted_body"]))
         text = utf16_surrogate.remove(parsed.text)
         mentions_by_user: dict[Long, MentionStruct] = {}