feat: 初始化高校人事请假考勤技能 (process-leave-attendance-default)

基于 skill-template 脚手架开发，包含：
- 5 张业务表（教职工、请假政策、考勤日历、请假记录、假期余额）
- 请假核算引擎（扣薪计算、审批层级判定、年假抵扣）
- CLI 入口（import-employees / calculate-leave / render-html）
- HTML 审批与扣薪报告生成
- 示例数据与完整测试套件（295 tests passed）

scripts/db/timestamp_columns.py

@@ -0,0 +1,50 @@
+"""标准时间字段：Unix 秒级时间戳、默认值与 updated_at 自动维护。
+
+业务表若包含 created_at / updated_at，在 CREATE TABLE 后调用
+``init_updated_at_trigger(cursor, table_name)``。模板默认不建业务表。
+"""
+
+from __future__ import annotations
+
+STANDARD_TIMESTAMP_COLUMNS = frozenset({"created_at", "updated_at"})
+DATETIME_UNIX_SECONDS = "datetime_unix_seconds"
+
+
+def updated_at_trigger_name(table_name: str) -> str:
+    return f"{table_name}_set_updated_at"
+
+
+def _quote_identifier(name: str) -> str:
+    return '"' + name.replace('"', '""') + '"'
+
+
+def init_updated_at_trigger(cursor, table_name: str) -> None:
+    """幂等创建 {table}_set_updated_at：业务字段 UPDATE 后刷新 updated_at。"""
+    trigger = updated_at_trigger_name(table_name)
+    quoted = _quote_identifier(table_name)
+    quoted_trigger = _quote_identifier(trigger)
+    cursor.execute(
+        f"""
+CREATE TRIGGER IF NOT EXISTS {quoted_trigger}
+AFTER UPDATE ON {quoted}
+FOR EACH ROW
+BEGIN
+    UPDATE {quoted}
+    SET updated_at = unixepoch()
+    WHERE id = NEW.id AND updated_at = OLD.updated_at;
+END
+"""
+    )
+
+
+def has_updated_at_trigger(cursor, table_name: str) -> bool:
+    trigger_name = updated_at_trigger_name(table_name)
+    cursor.execute(
+        """
+        SELECT 1 FROM sqlite_master
+        WHERE type = 'trigger' AND name = ? AND tbl_name = ?
+        LIMIT 1
+        """,
+        (trigger_name, table_name),
+    )
+    return cursor.fetchone() is not None