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/tests/control/admin/billing.rs

@@ -131,9 +131,9 @@ async fn gateway_handles_admin_billing_apply_preset_locally_with_trusted_admin_p
     let gateway = build_router_with_state(
         AppState::new()
             .expect("gateway should build")
-            .with_admin_billing_collectors_for_tests(Vec::<
-                crate::AdminBillingCollectorRecord,
-            >::new()),
+            .with_admin_billing_collectors_for_tests(
+                Vec::<crate::AdminBillingCollectorRecord>::new(),
+            ),
     );
     let (gateway_url, gateway_handle) = start_server(gateway).await;
 
@@ -215,11 +215,9 @@ async fn gateway_returns_conflict_for_admin_billing_apply_preset_when_backend_un
     let (upstream_url, upstream_handle) = start_server(upstream).await;
     let mut state = AppState::new()
         .expect("gateway should build")
-        .with_data_state_for_tests(
-            crate::data::GatewayDataState::with_user_reader_for_tests(Arc::new(
-                InMemoryUserReadRepository::seed_auth_users(Vec::new()),
-            )),
-        );
+        .with_data_state_for_tests(crate::data::GatewayDataState::with_user_reader_for_tests(
+            Arc::new(InMemoryUserReadRepository::seed_auth_users(Vec::new())),
+        ));
     state.admin_billing_collector_store = None;
     let gateway = build_router_with_state(state);
     let (gateway_url, gateway_handle) = start_server(gateway).await;
@@ -443,11 +441,9 @@ async fn gateway_returns_conflict_for_admin_billing_rule_create_when_backend_una
     let (upstream_url, upstream_handle) = start_server(upstream).await;
     let mut state = AppState::new()
         .expect("gateway should build")
-        .with_data_state_for_tests(
-            crate::data::GatewayDataState::with_user_reader_for_tests(Arc::new(
-                InMemoryUserReadRepository::seed_auth_users(Vec::new()),
-            )),
-        );
+        .with_data_state_for_tests(crate::data::GatewayDataState::with_user_reader_for_tests(
+            Arc::new(InMemoryUserReadRepository::seed_auth_users(Vec::new())),
+        ));
     state.admin_billing_rule_store = None;
     let gateway = build_router_with_state(state);
     let (gateway_url, gateway_handle) = start_server(gateway).await;