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/state/oauth.rs

@@ -64,10 +64,8 @@ impl AppState {
         provider_id: &str,
         endpoint_id: &str,
         key_id: &str,
-    ) -> Result<
-        Option<crate::provider_transport::GatewayProviderTransportSnapshot>,
-        GatewayError,
-    > {
+    ) -> Result<Option<crate::provider_transport::GatewayProviderTransportSnapshot>, GatewayError>
+    {
         self.data
             .read_provider_transport_snapshot(provider_id, endpoint_id, key_id)
             .await
@@ -318,10 +316,8 @@ impl AppState {
         provider_id: &str,
         endpoint_id: &str,
         key_id: &str,
-    ) -> Result<
-        Option<crate::provider_transport::GatewayProviderTransportSnapshot>,
-        GatewayError,
-    > {
+    ) -> Result<Option<crate::provider_transport::GatewayProviderTransportSnapshot>, GatewayError>
+    {
         let Some(cache_key) =
             ProviderTransportSnapshotCacheKey::new(provider_id, endpoint_id, key_id)
         else {