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/runtime/candidate_queries.rs

@@ -1,13 +1,11 @@
 use crate::{AppState, GatewayError};
+use aether_data_contracts::repository::{candidate_selection, candidates, quota};
 
 impl AppState {
     pub(crate) async fn list_minimal_candidate_selection_rows_for_api_format(
         &self,
         api_format: &str,
-    ) -> Result<
-        Vec<aether_data::repository::candidate_selection::StoredMinimalCandidateSelectionRow>,
-        GatewayError,
-    > {
+    ) -> Result<Vec<candidate_selection::StoredMinimalCandidateSelectionRow>, GatewayError> {
         self.data
             .list_minimal_candidate_selection_rows_for_api_format(api_format)
             .await
@@ -18,10 +16,7 @@ impl AppState {
         &self,
         api_format: &str,
         global_model_name: &str,
-    ) -> Result<
-        Vec<aether_data::repository::candidate_selection::StoredMinimalCandidateSelectionRow>,
-        GatewayError,
-    > {
+    ) -> Result<Vec<candidate_selection::StoredMinimalCandidateSelectionRow>, GatewayError> {
         self.data
             .list_minimal_candidate_selection_rows(api_format, global_model_name)
             .await
@@ -31,8 +26,7 @@ impl AppState {
     pub(crate) async fn read_provider_quota_snapshot(
         &self,
         provider_id: &str,
-    ) -> Result<Option<aether_data::repository::quota::StoredProviderQuotaSnapshot>, GatewayError>
-    {
+    ) -> Result<Option<quota::StoredProviderQuotaSnapshot>, GatewayError> {
         self.data
             .find_provider_quota_by_provider_id(provider_id)
             .await
@@ -42,8 +36,7 @@ impl AppState {
     pub(crate) async fn read_recent_request_candidates(
         &self,
         limit: usize,
-    ) -> Result<Vec<aether_data::repository::candidates::StoredRequestCandidate>, GatewayError>
-    {
+    ) -> Result<Vec<candidates::StoredRequestCandidate>, GatewayError> {
         self.data
             .list_recent_request_candidates(limit)
             .await
@@ -52,9 +45,8 @@ impl AppState {
 
     pub(crate) async fn upsert_request_candidate(
         &self,
-        candidate: aether_data::repository::candidates::UpsertRequestCandidateRecord,
-    ) -> Result<Option<aether_data::repository::candidates::StoredRequestCandidate>, GatewayError>
-    {
+        candidate: candidates::UpsertRequestCandidateRecord,
+    ) -> Result<Option<candidates::StoredRequestCandidate>, GatewayError> {
         self.data
             .upsert_request_candidate(candidate)
             .await