refactor: 大规模模块拆分与代码精简，新增 ai-pipeline/data-contracts 独立 crate

- 新增 aether-ai-pipeline 和 aether-data-contracts crate，将 pipeline 逻辑与数据契约从 gateway 中解耦
- 重构 admin handlers：拆分单体模块为 auth/billing/endpoint/features/model/observability/provider/system 等独立子模块
- 合并 chat/cli 重复代码路径：精简 conversion、finalize、planner 中的 sync/chat/cli 分支
- 重构 scheduler/executor/data 层，引入 facade 模式降低模块间耦合
- 移除冗余的 intent 模块，将 plan_fallback/policy/stream_path/sync_path 迁移至 executor
- 前端适配：调整 admin API 调用和 provider 模型测试对话框

apps/aether-gateway/src/usage/worker.rs

@@ -4,7 +4,8 @@ pub(crate) use aether_usage_runtime::{build_usage_queue_worker, write_event_reco
 mod tests {
     use std::sync::Arc;
 
-    use aether_data::repository::usage::{InMemoryUsageReadRepository, UsageReadRepository};
+    use aether_data::repository::usage::InMemoryUsageReadRepository;
+    use aether_data_contracts::repository::usage::UsageReadRepository;
 
     use super::write_event_record;
     use crate::data::GatewayDataState;