fix: 号池列表统计与最后使用时间显示

- 为 usage 仓储新增按 provider_api_key_id 汇总请求数、Token、费用和最后使用时间的能力
- 在 /api/admin/pool/{provider_id}/keys 中优先使用 usage 汇总结果覆盖 request_count、total_tokens、total_cost_usd、last_used_at
- 补充数据层与网关侧回归测试，避免号池管理页统计全为 0 且最后使用为空

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

@@ -1,7 +1,7 @@
 mod types;
 
 pub use types::{
-    StoredProviderUsageSummary, StoredProviderUsageWindow, StoredRequestUsageAudit,
-    UpsertUsageRecord, UsageAuditListQuery, UsageReadRepository, UsageRepository,
-    UsageWriteRepository,
+    StoredProviderApiKeyUsageSummary, StoredProviderUsageSummary, StoredProviderUsageWindow,
+    StoredRequestUsageAudit, UpsertUsageRecord, UsageAuditListQuery, UsageReadRepository,
+    UsageRepository, UsageWriteRepository,
 };

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

@@ -279,6 +279,15 @@ pub struct StoredProviderUsageSummary {
     pub total_cost_usd: f64,
 }
 
+#[derive(Debug, Clone, PartialEq, Default, serde::Serialize, serde::Deserialize)]
+pub struct StoredProviderApiKeyUsageSummary {
+    pub provider_api_key_id: String,
+    pub request_count: u64,
+    pub total_tokens: u64,
+    pub total_cost_usd: f64,
+    pub last_used_at_unix_secs: Option<u64>,
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, Default, serde::Serialize, serde::Deserialize)]
 pub struct UsageAuditListQuery {
     pub created_from_unix_secs: Option<u64>,
@@ -316,6 +325,14 @@ pub trait UsageReadRepository: Send + Sync {
         api_key_ids: &[String],
     ) -> Result<std::collections::BTreeMap<String, u64>, crate::DataLayerError>;
 
+    async fn summarize_usage_by_provider_api_key_ids(
+        &self,
+        provider_api_key_ids: &[String],
+    ) -> Result<
+        std::collections::BTreeMap<String, StoredProviderApiKeyUsageSummary>,
+        crate::DataLayerError,
+    >;
+
     async fn summarize_provider_usage_since(
         &self,
         provider_id: &str,