fix: enable rich markup in chat log

RichLog defaults markup=False, so all Rich console markup tags
([dim], [#9ece6a], etc.) rendered as literal text. Pass
markup=True in ChatLog constructor.

src/tuimble/app.py

@@ -186,7 +186,8 @@ class ChannelTree(Static):
 class ChatLog(RichLog):
     """Message log."""
 
-    pass
+    def __init__(self, **kwargs) -> None:
+        super().__init__(markup=True, **kwargs)
 
 
 # -- main app ----------------------------------------------------------------