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

frontend/src/api/endpoints/endpoints.ts

@@ -75,6 +75,6 @@ export async function deleteEndpoint(endpointId: string): Promise<{ message: str
 export async function getDefaultBodyRules(apiFormat: string, providerType?: string): Promise<{ api_format: string; body_rules: BodyRule[] }> {
   const params: Record<string, string> = {}
   if (providerType) params.provider_type = providerType
-  const response = await client.get(`/api/admin/endpoints/defaults/${encodeURIComponent(apiFormat)}/body-rules`, { params })
+  const response = await client.get(`/api/admin/endpoints/defaults/${apiFormat}/body-rules`, { params })
   return response.data
 }

frontend/src/api/endpoints/providers.ts

@@ -194,6 +194,7 @@ export interface TestModelFailoverRequest {
   provider_id: string
   mode: 'global' | 'direct'
   model_name: string
+  failover_models?: string[]
   api_format?: string
   endpoint_id?: string
   message?: string
@@ -239,7 +240,14 @@ export async function testModelFailover(
   data: TestModelFailoverRequest,
   options: { signal?: AbortSignal } = {}
 ): Promise<TestModelFailoverResponse> {
-  const response = await client.post('/api/admin/provider-query/test-model-failover', data, {
+  const normalizedModelName = typeof data.model_name === 'string' ? data.model_name.trim() : ''
+  const failoverModels = Array.isArray(data.failover_models) && data.failover_models.length > 0
+    ? data.failover_models
+    : (normalizedModelName ? [normalizedModelName] : undefined)
+  const response = await client.post('/api/admin/provider-query/test-model-failover', {
+    ...data,
+    ...(failoverModels ? { failover_models: failoverModels } : {}),
+  }, {
     timeout: 10 * 60 * 1000,
     signal: options.signal,
   })