接入微信一键登录服务端接口

改动内容：新增微信 code 换 openid 集成、/api/v1/auth/wechat-login 登录接口、微信用户创建/复用逻辑和测试覆盖。

验证方式：python -m pytest tests\\test_auth.py tests\\test_health.py -q 通过。

tests/test_auth.py

@@ -68,6 +68,68 @@ def test_sms_login_and_me_flow(client) -> None:
     assert r.json()["ok"] is True
 
 
+def test_wechat_login_creates_and_reuses_user(client, monkeypatch) -> None:
+    def fake_code_to_userinfo(code: str) -> dict:
+        return {
+            "openid": "openid-login-create",
+            "unionid": "union-login-create",
+            "nickname": "微信昵称",
+            "avatar_url": "https://wx.example/avatar.png",
+            "raw": {"code": code},
+        }
+
+    monkeypatch.setattr("app.api.v1.auth.code_to_userinfo", fake_code_to_userinfo)
+
+    r = client.post("/api/v1/auth/wechat-login", json={"code": "code-a", "device_id": "dev-wx"})
+    assert r.status_code == 200, r.text
+    first = r.json()
+    assert first["user"]["register_channel"] == "wechat"
+    assert first["user"]["phone"].startswith("wx_")
+    assert first["user"]["nickname"] == "微信昵称"
+
+    r = client.post("/api/v1/auth/wechat-login", json={"code": "code-b", "device_id": "dev-wx"})
+    assert r.status_code == 200, r.text
+    second = r.json()
+    assert second["user"]["id"] == first["user"]["id"]
+    assert second["user"]["phone"] == first["user"]["phone"]
+
+
+def test_wechat_login_uses_existing_bound_user(client, monkeypatch) -> None:
+    from app.db.session import SessionLocal
+    from app.repositories import user as user_repo
+
+    db = SessionLocal()
+    try:
+        user = user_repo.upsert_user_for_login(
+            db,
+            phone="13600136000",
+            register_channel="sms",
+        )
+        user.wechat_openid = "openid-login-bound"
+        user.wechat_nickname = "已绑定昵称"
+        db.commit()
+        user_id = user.id
+    finally:
+        db.close()
+
+    def fake_code_to_userinfo(code: str) -> dict:
+        return {
+            "openid": "openid-login-bound",
+            "unionid": "union-login-bound",
+            "nickname": "新微信昵称",
+            "avatar_url": None,
+            "raw": {"code": code},
+        }
+
+    monkeypatch.setattr("app.api.v1.auth.code_to_userinfo", fake_code_to_userinfo)
+
+    r = client.post("/api/v1/auth/wechat-login", json={"code": "code-bound", "device_id": "dev-wx"})
+    assert r.status_code == 200, r.text
+    body = r.json()
+    assert body["user"]["id"] == user_id
+    assert body["user"]["phone"] == "13600136000"
+
+
 def test_sms_send_too_frequent(client) -> None:
     phone = "13900139000"
     assert client.post("/api/v1/auth/sms/send", json={"phone": phone}).status_code == 200