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/public/system_modules_helpers.rs

@@ -13,22 +13,12 @@ pub(crate) use self::system_modules_capabilities::{
 };
 pub(crate) use self::system_modules_keys_grouped::build_admin_keys_grouped_by_format_payload;
 pub(crate) use self::system_modules_modules::{
-    admin_module_by_name, admin_module_name_from_enabled_path, admin_module_name_from_status_path,
-    build_admin_module_runtime_state, build_admin_module_status_payload,
-    build_admin_module_validation_result, build_admin_modules_status_payload,
     build_public_auth_modules_status_payload, ldap_module_config_is_valid,
-    AdminSetModuleEnabledRequest,
 };
 pub(crate) use self::system_modules_system::{
-    apply_admin_email_template_update, apply_admin_system_config_update,
-    apply_admin_system_settings_update, build_admin_api_formats_payload,
-    build_admin_email_template_payload, build_admin_email_templates_payload,
-    build_admin_system_check_update_payload, build_admin_system_config_detail_payload,
-    build_admin_system_config_export_payload, build_admin_system_configs_payload,
-    build_admin_system_settings_payload, build_admin_system_stats_payload,
-    build_admin_system_users_export_payload, current_aether_version, delete_admin_system_config,
-    escape_admin_email_template_html, module_available_from_env, preview_admin_email_template,
-    read_admin_email_template_payload, render_admin_email_template_html,
-    reset_admin_email_template, serialize_admin_system_users_export_wallet, system_config_bool,
+    apply_admin_email_template_update, build_admin_email_template_payload,
+    build_admin_email_templates_payload, escape_admin_email_template_html,
+    module_available_from_env, preview_admin_email_template, read_admin_email_template_payload,
+    render_admin_email_template_html, reset_admin_email_template, system_config_bool,
     system_config_string,
 };