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/observability/usage/mod.rs

@@ -0,0 +1,53 @@
+use crate::control::GatewayPublicRequestContext;
+use crate::{AppState, GatewayError};
+use axum::{
+    body::Body,
+    response::{IntoResponse, Response},
+};
+
+mod analytics;
+mod analytics_routes;
+mod detail_routes;
+mod helpers;
+mod replay;
+mod summary_routes;
+
+pub(crate) async fn maybe_build_local_admin_usage_response(
+    state: &AppState,
+    request_context: &GatewayPublicRequestContext,
+    request_body: Option<&axum::body::Bytes>,
+) -> Result<Option<Response<Body>>, GatewayError> {
+    let Some(decision) = request_context.control_decision.as_ref() else {
+        return Ok(None);
+    };
+
+    if decision.route_family.as_deref() != Some("usage_manage") {
+        return Ok(None);
+    }
+
+    if let Some(response) = detail_routes::maybe_build_local_admin_usage_detail_response(
+        state,
+        request_context,
+        request_body,
+    )
+    .await?
+    {
+        return Ok(Some(response));
+    }
+
+    if let Some(response) =
+        summary_routes::maybe_build_local_admin_usage_summary_response(state, request_context)
+            .await?
+    {
+        return Ok(Some(response));
+    }
+
+    if let Some(response) =
+        analytics_routes::maybe_build_local_admin_usage_analytics_response(state, request_context)
+            .await?
+    {
+        return Ok(Some(response));
+    }
+
+    Ok(None)
+}