refactor: 清理旧数据库文件并完成导入更新

- 将6个旧数据库文件移动到 old/ 目录归档
  * sqlalchemy_models.py
  * sqlalchemy_database_api.py
  * database.py
  * db_migration.py
  * db_batch_scheduler.py
  * sqlalchemy_init.py
- 更新剩余2个文件的导入路径
  * src/schedule/database.py
  * src/plugins/built_in/napcat_adapter_plugin/src/database.py
- 数据库重构基本完成，系统使用新的6层架构

src/plugins/built_in/napcat_adapter_plugin/src/database.py

@@ -18,7 +18,8 @@ from typing import List, Optional, Sequence
 from sqlalchemy import BigInteger, Column, Index, Integer, UniqueConstraint, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from src.common.database.sqlalchemy_models import Base, get_db_session
+from src.common.database.core.models import Base
+from src.common.database.core import get_db_session
 from src.common.logger import get_logger
 
 logger = get_logger("napcat_adapter")

src/schedule/database.py

@@ -3,7 +3,8 @@
 
 from sqlalchemy import delete, func, select, update
 
-from src.common.database.sqlalchemy_models import MonthlyPlan, get_db_session
+from src.common.database.core.models import MonthlyPlan
+from src.common.database.core import get_db_session
 from src.common.logger import get_logger
 from src.config.config import global_config