Silently log LLM failures instead of replying to user

When the LLM is offline, post to #bcs-log instead of sending
the "brain offline" message in chat.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cogs/chat.py

@@ -119,7 +119,17 @@ class ChatCog(commands.Cog):
             await typing_ctx.__aexit__(None, None, None)
 
         if response is None:
-            response = "I'd roast you but my brain is offline. Try again later."
+            log_channel = discord.utils.get(message.guild.text_channels, name="bcs-log")
+            if log_channel:
+                try:
+                    await log_channel.send(
+                        f"**LLM OFFLINE** | Failed to generate reply to "
+                        f"{message.author.mention} in #{message.channel.name}"
+                    )
+                except discord.HTTPException:
+                    pass
+            logger.warning("LLM returned no response for %s in #%s", message.author, message.channel.name)
+            return
 
         if not image_attachment:
             self._chat_history[ch_id].append(