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/endpoint/mod.rs

@@ -0,0 +1,50 @@
+use crate::control::GatewayPublicRequestContext;
+use crate::{AppState, GatewayError};
+use axum::body::{Body, Bytes};
+use axum::http::Response;
+
+mod extractors;
+mod health;
+mod health_builders;
+mod keys;
+mod routes;
+mod rpm;
+
+pub(crate) use self::health_builders::build_admin_endpoint_health_status_payload;
+
+pub(crate) async fn maybe_build_local_admin_endpoints_response(
+    state: &AppState,
+    request_context: &GatewayPublicRequestContext,
+    request_body: Option<&Bytes>,
+) -> Result<Option<Response<Body>>, GatewayError> {
+    if let Some(response) =
+        health::maybe_build_local_admin_endpoints_health_response(state, request_context).await?
+    {
+        return Ok(Some(response));
+    }
+
+    if let Some(response) =
+        rpm::maybe_build_local_admin_endpoints_rpm_response(state, request_context).await?
+    {
+        return Ok(Some(response));
+    }
+
+    if let Some(response) =
+        keys::maybe_build_local_admin_endpoints_keys_response(state, request_context, request_body)
+            .await?
+    {
+        return Ok(Some(response));
+    }
+
+    if let Some(response) = routes::maybe_build_local_admin_endpoints_routes_response(
+        state,
+        request_context,
+        request_body,
+    )
+    .await?
+    {
+        return Ok(Some(response));
+    }
+
+    Ok(None)
+}