fix(admin): 修复 usage 观测全表扫描并下推聚合查询

- 收紧 admin usage/stats 默认时间范围和 active 轮询查询
- 将 summary/records/aggregation/time-series/leaderboard 下推到 SQL 侧
- 统一前端时间参数并补齐 admin usage/stats 回归测试

apps/aether-gateway/src/handlers/admin/observability/stats/mod.rs

@@ -10,6 +10,7 @@ mod provider_quota_routes;
 mod range;
 pub(crate) use self::range::{
     list_usage_for_optional_range, list_usage_for_range, parse_bounded_u32,
+    resolve_admin_usage_time_range,
 };
 pub(crate) use aether_admin::observability::stats::{
     admin_stats_bad_request_response, aggregate_usage_stats, round_to, AdminStatsTimeRange,