Fix/usage transfer filter (#307)

* fix(usage): 恢复 usage 列表中的 fallback 路由信号

* fix(admin): 支持 usage 记录展示和筛选 fallback 转移

* fix(usage): 在用户 usage 记录中暴露 fallback 标记

* fix(usage): 共享 usage 页面支持 fallback 筛选

* fix(usage): 对齐 fallback 筛选相关前端类型

* fix(usage): propagate has_fallback through active polling

---------

Co-authored-by: fawney19 <elky0401@gmail.com>

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

@@ -361,6 +361,11 @@ impl StoredRequestUsageAudit {
             .or_else(|| self.request_metadata_u64("candidate_index"))
     }
 
+    pub fn has_fallback(&self) -> bool {
+        self.routing_candidate_index()
+            .is_some_and(|index| index > 0)
+    }
+
     pub fn routing_key_name(&self) -> Option<&str> {
         self.key_name
             .as_deref()