fix(usage): 完善 cache-affinity 时间线的用户名回退与模型空值兜底

- 当 auth 用户查询失败时回退到历史 username，避免时间线丢失用户信息
- SQL 投影对 usage.model 使用 COALESCE 兜底空值
- IntervalTimelineCard 在刷新间隔为 0 时跳过定时刷新
- Usage 页面关闭时间线卡片的自动轮询

crates/aether-data/src/repository/usage/sql.rs

@@ -2495,7 +2495,7 @@ WITH filtered_usage AS (
         builder.push(
             r#" AS group_id,
     "usage".username AS username,
-    "usage".model AS model,
+    COALESCE("usage".model, '') AS model,
     "usage".created_at AS created_at,
     "usage".id AS usage_id
   FROM "usage"
@@ -6188,6 +6188,11 @@ mod tests {
         assert!(super::LIST_RECENT_USAGE_AUDITS_PREFIX.contains("FROM \"usage\""));
     }
 
+    #[test]
+    fn usage_sql_cache_affinity_interval_query_coalesces_nullable_model_values() {
+        assert!(include_str!("sql.rs").contains("COALESCE(\"usage\".model, '') AS model"));
+    }
+
     #[test]
     fn usage_sql_reads_http_audits_for_single_record_fetches() {
         assert!(super::FIND_BY_REQUEST_ID_SQL.contains("LEFT JOIN usage_http_audits"));