perf(usage): user-me usage 查询避免全量加载，默认限制 7 天范围

- UsageAuditListQuery 新增 limit 字段，支持在 SQL 层 LIMIT
- user-me usage 端点无时间范围时默认查最近 7 天
- active usage 端点无 ids 过滤时限制查最近 1 小时
- InMemory 实现同步支持 limit truncate

crates/aether-data-contracts/src/repository/usage/types.rs

@@ -481,6 +481,7 @@ pub struct UsageAuditListQuery {
     pub provider_name: Option<String>,
     pub model: Option<String>,
     pub statuses: Option<Vec<String>>,
+    pub limit: Option<usize>,
 }
 
 #[derive(Debug, Clone, PartialEq, Default, serde::Serialize, serde::Deserialize)]