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

tests/test_postgres.py

@@ -0,0 +1,74 @@
+"""PostgreSQL 后端集成测试（需 CHONGMING_TEST_PG_URL 环境变量，否则跳过）。"""
+
+import os
+import uuid
+
+import pytest
+from sqlmodel import Field, SQLModel, select
+
+from chongming_database import Database
+
+PG_URL = os.environ.get("CHONGMING_TEST_PG_URL")
+
+pytestmark = pytest.mark.skipif(
+    not PG_URL, reason="CHONGMING_TEST_PG_URL 未设置，跳过 PostgreSQL 集成测试"
+)
+
+
+def _make_item_table(tablename: str):
+    """动态生成随机表名的 SQLModel 表，避免污染共享 PG 实例。"""
+
+    class Item(SQLModel, table=True):
+        __tablename__ = tablename
+
+        id: int | None = Field(default=None, primary_key=True)
+        name: str = Field(max_length=50)
+
+    return Item
+
+
+async def test_postgres_crud():
+    Item = _make_item_table(f"pg_test_item_{uuid.uuid4().hex[:8]}")
+    db = Database.from_url(PG_URL)
+    await db.initialize()
+    try:
+        async with db.get_session() as session:
+            session.add(Item(name="pg"))
+            await session.commit()
+        async with db.get_session() as session:
+            rows = (await session.execute(select(Item))).scalars().all()
+            assert [r.name for r in rows] == ["pg"]
+    finally:
+        await db.dispose()
+
+
+async def test_postgres_bare_url_scheme():
+    """裸 postgresql:// 应被归一化为 postgresql+asyncpg:// 后正常连接。"""
+    bare = PG_URL.replace("postgresql+asyncpg://", "postgresql://", 1)
+    db = Database.from_url(bare)
+    await db.initialize()
+    try:
+        async with db.get_session() as session:
+            await session.execute(select(1))
+    finally:
+        await db.dispose()
+
+
+async def test_from_config_postgres_end_to_end():
+    db = Database.from_config({"type": "postgresql", "url": PG_URL})
+    await db.initialize()
+    try:
+        async with db.get_session() as session:
+            await session.execute(select(1))
+    finally:
+        await db.dispose()
+
+
+async def test_postgres_generate_schemas_false():
+    db = Database.from_url(PG_URL)
+    await db.initialize(generate_schemas=False)
+    try:
+        async with db.get_session() as session:
+            await session.execute(select(1))
+    finally:
+        await db.dispose()