fix: add bcrypt version constraint for passlib compatibility

bcrypt 5.0.0 is incompatible with passlib 1.7.x - passlib tries to
access bcrypt.__about__.__version__ which was removed in bcrypt 5.x.

Constrain bcrypt to >=4.0,<5.0 to maintain compatibility.

src/backend/app/services/ai_agent/__init__.py

@@ -1,4 +1,4 @@
-from .crew import CrewAgent
-from .llm_connector import LLMConnector
+from .crew import TradingCrew, get_trading_crew
+from .llm_connector import MiniMaxLLM, MiniMaxConnector
 
-__all__ = ["CrewAgent", "LLMConnector"]
+__all__ = ["TradingCrew", "get_trading_crew", "MiniMaxLLM", "MiniMaxConnector"]

src/backend/app/services/ai_agent/crew.py

@@ -1,7 +1,7 @@
 from typing import List, Optional, Dict, Any
 from crewai import Agent, Task, Crew
 from .llm_connector import MiniMaxConnector, MiniMaxLLM
-from ..core.config import get_settings
+from ...core.config import get_settings
 
 
 class StrategyValidator:

src/backend/requirements.txt

@@ -6,6 +6,7 @@ pydantic-settings>=2.1.0
 email-validator>=2.0.0
 python-jose[cryptography]>=3.3.0
 passlib[bcrypt]>=1.7.4
+bcrypt>=4.0,<5.0  # Required for passlib compatibility
 crewai>=0.1.0
 anthropic>=0.18.0
 httpx>=0.26.0