refactor: consolidate conversation_history to ConversationHistory class

Remove legacy globals.conversation_history (defaultdict of deques) and
route all callers through utils.conversation_history.ConversationHistory:

- globals.py: remove conversation_history + unused collections imports
- llm.py: remove backward-compat dual-write to legacy system
- api.py: /conversation/{user_id} now reads from ConversationHistory
- actions.py: reset_conversation uses clear_channel()
- figurine_notifier.py: use add_message() instead of buggy setdefault()
- bipolar_mode.py: fix clear_history -> clear_channel (was AttributeError
  silently swallowed by bare except), fix bare except -> except Exception

bot/utils/figurine_notifier.py

@@ -5,8 +5,8 @@ from datetime import datetime
 from typing import List, Dict, Any, Tuple
 
 import discord
-import globals
 
+from utils.conversation_history import conversation_history
 from utils.twitter_fetcher import fetch_figurine_tweets_latest
 from utils.image_handling import analyze_image_with_qwen, download_and_encode_image
 from utils.llm import query_llama
@@ -204,15 +204,11 @@ async def send_figurine_dm_to_user(client: discord.Client, user_id: int, tweet:
         # Log the comment message
         dm_logger.log_user_message(user, comment_message, is_bot_message=True)
         
-        # IMPORTANT: Also add to globals.conversation_history for LLM context
+        # Add to conversation history for LLM context (uses centralized ConversationHistory)
         user_id_str = str(user_id)
-        
-        # Add the tweet URL as a "system message" about what Miku just sent (use original URL for context)
         tweet_context = f"[I just sent you this figurine tweet: {tweet_url}]"
-        
-        # Add the figurine comment to conversation history 
-        # Use empty user prompt since this was initiated by Miku
-        globals.conversation_history.setdefault(user_id_str, []).append((tweet_context, miku_comment))
+        conversation_history.add_message(channel_id=user_id_str, author_name="Miku", content=tweet_context, is_bot=True)
+        conversation_history.add_message(channel_id=user_id_str, author_name="Miku", content=miku_comment, is_bot=True)
         
         logger.debug(f"Messages logged to both DM history and conversation context for user {user_id}")