refactor(audit): 移除旧格式兼容，user_id 统一走列字段

- audit_log 查询去掉 detail->>'user_id' 回退分支
- login_detail 不再冗余写入 user_id 到 detail JSON
- 迁移 SQL 去掉多余的 ALTER TABLE ADD COLUMN

Made-with: Cursor

crates/secrets-core/src/service/audit_log.rs

@@ -10,7 +10,7 @@ pub async fn list_for_user(pool: &PgPool, user_id: Uuid, limit: i64) -> Result<V
     let rows = sqlx::query_as(
         "SELECT id, user_id, action, namespace, kind, name, detail, actor, created_at \
          FROM audit_log \
-         WHERE user_id = $1 OR (user_id IS NULL AND detail->>'user_id' = $1::text) \
+         WHERE user_id = $1 \
          ORDER BY created_at DESC, id DESC \
          LIMIT $2",
     )