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/async_task/http.rs

@@ -1,7 +1,7 @@
 use std::time::{SystemTime, UNIX_EPOCH};
 
 use aether_contracts::ExecutionResult;
-use aether_data::repository::video_tasks::{
+use aether_data_contracts::repository::video_tasks::{
     StoredVideoTask, VideoTaskQueryFilter, VideoTaskStatus,
 };
 use axum::body::Body;
@@ -63,7 +63,7 @@ pub(crate) async fn get_video_task_stats(
 pub(crate) async fn get_video_task_detail(
     State(state): State<AppState>,
     Path(task_id): Path<String>,
-) -> Result<Json<aether_data::repository::video_tasks::StoredVideoTask>, axum::response::Response> {
+) -> Result<Json<StoredVideoTask>, axum::response::Response> {
     let task = read_video_task_detail(&state, &task_id)
         .await
         .map_err(IntoResponse::into_response)?;