feat(memory): add memory config caching to end_user model

- Add memory_config_id field to EndUser model for lazy caching of memory configuration
- Create get_end_user_memory_config_id() function for fast retrieval of cached config ID
- Implement lazy update mechanism in get_end_user_connected_config() to cache memory_config_id
- Optimize memory config lookup by storing config ID directly on end_user record
- Improve import organization and formatting in memory_agent_service.py
- Add indexed foreign key relationship to data_config table for efficient queries

api/app/models/end_user_model.py

@@ -1,9 +1,11 @@
 import datetime
 import uuid
-from sqlalchemy import Column, String, DateTime, ForeignKey, Text, BigInteger
+
+from app.db import Base
+from sqlalchemy import BigInteger, Column, DateTime, ForeignKey, Integer, String, Text
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import relationship
-from app.db import Base
+
 
 class EndUser(Base):
     __tablename__ = "end_users"
@@ -18,6 +20,9 @@ class EndUser(Base):
     created_at = Column(DateTime, default=datetime.datetime.now)
     updated_at = Column(DateTime, default=datetime.datetime.now, onupdate=datetime.datetime.now)
     
+    # Memory config association - updated lazily during conversation
+    memory_config_id = Column(Integer, ForeignKey("data_config.config_id"), nullable=True, index=True, comment="关联的记忆配置ID")
+    
     # 用户基本信息字段
     position = Column(String, nullable=True, comment="职位")
     department = Column(String, nullable=True, comment="部门")