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/handlers/admin/provider/oauth/mod.rs

@@ -0,0 +1,16 @@
+mod dispatch;
+pub(crate) mod quota;
+pub(crate) mod refresh;
+pub(crate) mod state;
+
+pub(crate) use self::dispatch::maybe_build_local_admin_provider_oauth_response;
+pub(crate) use self::quota as provider_oauth_quota;
+pub(crate) use self::quota::{
+    normalize_string_id_list, refresh_antigravity_provider_quota_locally,
+    refresh_codex_provider_quota_locally, refresh_kiro_provider_quota_locally,
+};
+pub(crate) use self::refresh as provider_oauth_refresh;
+pub(crate) use self::refresh::{
+    build_internal_control_error_response, normalize_provider_oauth_refresh_error_message,
+};
+pub(crate) use self::state as provider_oauth_state;