- Add Conversation model with user/anonymous_token/bot_id fields
- Add Message model linked to conversations
- Add AnonymousUser model for tracking anonymous chat limits
- Create /api/conversations endpoints (list, create, get, delete)
- Add POST /api/conversations/{id}/chat for messaging
- Add POST /api/conversations/{id}/set-bot for linking bot
- Implement rate limiter with system-wide (500/5hrs) and anonymous limits
- Anonymous users: max 50 chats, max 1 bot, max 1 backtest
- Add warning after 40 anonymous messages
- Register conversations router in main.py
- Add create_bot, list_bots, set_bot, get_bot_info tools to registry
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