fix: 兼容 corp_id 字段不存在 + 添加迁移 API

backend/app/routers/tenants.py

@@ -83,7 +83,7 @@ async def list_tenants(
                 "id": t.id,
                 "code": t.code,
                 "name": t.name,
-                "corp_id": t.corp_id,
+                "corp_id": getattr(t, 'corp_id', None),
                 "contact_info": t.contact_info,
                 "status": t.status,
                 "expired_at": t.expired_at,
@@ -123,7 +123,7 @@ async def get_tenant(
         "id": tenant.id,
         "code": tenant.code,
         "name": tenant.name,
-        "corp_id": tenant.corp_id,
+        "corp_id": getattr(tenant, 'corp_id', None),
         "contact_info": tenant.contact_info,
         "status": tenant.status,
         "expired_at": tenant.expired_at,