fix: convert remaining f-string logger calls to loguru native format

Follow-up to #864. Three f-string logger calls in base.py and dingtalk.py
were missed in the original sweep. These can cause KeyError if interpolated
values contain curly braces, since loguru interprets them as format placeholders.

nanobot/channels/base.py

@@ -105,8 +105,9 @@ class BaseChannel(ABC):
         """
         if not self.is_allowed(sender_id):
             logger.warning(
-                f"Access denied for sender {sender_id} on channel {self.name}. "
-                f"Add them to allowFrom list in config to grant access."
+                "Access denied for sender {} on channel {}. "
+                "Add them to allowFrom list in config to grant access.",
+                sender_id, self.name,
             )
             return