feat(gateway/data): 新增 usage 关键词搜索、缓存命中摘要、结算成本摘要及 dashboard 聚合查询能力

- 新增 UsageAuditKeywordSearchQuery，支持多关键词、用户名、API Key 交叉过滤
- 新增 UsageCacheHitSummaryQuery/StoredUsageCacheHitSummary，统计请求缓存命中率
- 新增 UsageSettledCostSummaryQuery/StoredUsageSettledCostSummary，汇总结算成本
- 新增 UsageDashboardSummaryQuery、UsageBreakdownSummaryQuery 等 dashboard 聚合类型
- SQL 层实现对应查询方法，含 list_by_ids、list_usage_audits_by_keyword_search、count_usage_audits_by_keyword_search
- 将上述能力通过 GatewayDataState / AdminAppState 暴露给 handler 层
- user_me_usage 及 dashboard_filters 切换为新查询接口，移除旧的内存过滤逻辑
- 同步更新 memory 层及测试

crates/aether-data/src/repository/users/memory.rs

@@ -95,6 +95,29 @@ impl UserReadRepository for InMemoryUserReadRepository {
             .collect())
     }
 
+    async fn list_users_by_username_search(
+        &self,
+        username_search: &str,
+    ) -> Result<Vec<StoredUserSummary>, DataLayerError> {
+        let username_search = username_search.trim().to_ascii_lowercase();
+        if username_search.is_empty() {
+            return Ok(Vec::new());
+        }
+
+        Ok(self
+            .by_id
+            .read()
+            .expect("user repository lock")
+            .values()
+            .filter(|user| {
+                user.username
+                    .to_ascii_lowercase()
+                    .contains(&username_search)
+            })
+            .cloned()
+            .collect())
+    }
+
     async fn list_non_admin_export_users(
         &self,
     ) -> Result<Vec<StoredUserExportRow>, DataLayerError> {