后端第一步开发完成，第一版回归测试完成

backend/scripts/migrate_string_columns.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+"""
+将 projects 表中「质保期截止日」「中标合同金额」「工程款拨付方式」改为字符串类型。
+用法：cd backend && PYTHONPATH=src python3 scripts/migrate_string_columns.py
+"""
+import sys
+from pathlib import Path
+
+_backend = Path(__file__).resolve().parent.parent
+if str(_backend) not in sys.path:
+    sys.path.insert(0, str(_backend))
+
+from src.database import get_connection
+
+def main():
+    with get_connection() as conn:
+        cur = conn.cursor()
+        try:
+            cur.execute(
+                "ALTER TABLE projects "
+                "MODIFY COLUMN bid_contract_amount varchar(512) DEFAULT NULL COMMENT '中标合同金额（万元，字符串存储）', "
+                "MODIFY COLUMN warranty_end_date varchar(256) DEFAULT NULL COMMENT '质保期截止日（字符串存储）', "
+                "MODIFY COLUMN payment_method varchar(2048) DEFAULT NULL COMMENT '工程款拨付方式', "
+                "MODIFY COLUMN is_adjusted varchar(512) DEFAULT NULL COMMENT '是否调整：是/否'"
+            )
+            conn.commit()
+            print("已将 bid_contract_amount、warranty_end_date、payment_method、is_adjusted 改为目标类型/长度。")
+        except Exception as e:
+            print(f"迁移失败: {e}")
+            raise
+        finally:
+            cur.close()
+
+if __name__ == "__main__":
+    main()