feat: 初始化项目，并且接近完成 ozon 部分

server/db.py

@@ -0,0 +1,47 @@
+"""数据库：SQLite（aiosqlite）+ SQLAlchemy async。"""
+from __future__ import annotations
+
+from collections.abc import AsyncGenerator
+
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+
+from config import get_settings
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+_engine = None
+_session_factory: async_sessionmaker[AsyncSession] | None = None
+
+
+def get_engine():
+    global _engine, _session_factory
+    if _engine is None:
+        settings = get_settings()
+        db_path = f"{settings.data_dir}/app.db"
+        _engine = create_async_engine(f"sqlite+aiosqlite:///{db_path}", echo=False)
+        _session_factory = async_sessionmaker(_engine, expire_on_commit=False)
+    return _engine
+
+
+def get_session_factory() -> async_sessionmaker[AsyncSession]:
+    get_engine()
+    assert _session_factory is not None
+    return _session_factory
+
+
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
+    async with get_session_factory()() as session:
+        yield session
+
+
+async def init_db() -> None:
+    """启动时建表（MVP 不引 Alembic，模型变更删库重建即可）。"""
+    import models  # noqa: F401  确保模型注册
+
+    engine = get_engine()
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)