add: PostgreSQL 支持（asyncpg 驱动，from_url/from_config + 集成测试）

tests/test_sqlite.py

@@ -0,0 +1,71 @@
+"""SQLite 后端回归测试（tmp_path，无需外部服务）。"""
+
+from pathlib import Path
+
+import pytest
+from sqlmodel import Field, SQLModel, select
+
+from chongming_database import Database
+
+
+class SqliteItem(SQLModel, table=True):
+    __tablename__ = "backend_test_item"
+
+    id: int | None = Field(default=None, primary_key=True)
+    name: str = Field(max_length=50)
+
+
+async def test_sqlite_crud(tmp_path: Path):
+    db = Database(tmp_path / "nested" / "test.db")
+    await db.initialize()
+    try:
+        async with db.get_session() as session:
+            session.add(SqliteItem(name="a"))
+            await session.commit()
+        async with db.get_session() as session:
+            rows = (await session.execute(select(SqliteItem))).scalars().all()
+            assert [r.name for r in rows] == ["a"]
+    finally:
+        await db.dispose()
+
+
+async def test_sqlite_initialize_is_idempotent(tmp_path: Path):
+    """重复 initialize（模拟多进程各自初始化）不应报错。"""
+    db = Database(tmp_path / "test.db")
+    await db.initialize()
+    try:
+        await db.initialize()
+    finally:
+        await db.dispose()
+
+
+async def test_get_session_before_initialize_raises(tmp_path: Path):
+    db = Database(tmp_path / "test.db")
+    try:
+        with pytest.raises(RuntimeError):
+            db.get_session()
+    finally:
+        await db.dispose()
+
+
+async def test_from_config_sqlite_end_to_end(tmp_path: Path):
+    db = Database.from_config(
+        {"type": "sqlite", "database_path": str(tmp_path / "cfg.db")}
+    )
+    await db.initialize()
+    try:
+        async with db.get_session() as session:
+            await session.execute(select(SqliteItem))
+    finally:
+        await db.dispose()
+
+
+async def test_generate_schemas_false_skips_ddl(tmp_path: Path):
+    """generate_schemas=False 时只建引擎不建表，会话仍可用。"""
+    db = Database(tmp_path / "noschema.db")
+    await db.initialize(generate_schemas=False)
+    try:
+        async with db.get_session() as session:
+            await session.execute(select(1))
+    finally:
+        await db.dispose()