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/control/execute.rs

@@ -3,6 +3,7 @@ use axum::http::{HeaderName, HeaderValue, Response};
 
 use crate::constants::CONTROL_EXECUTED_HEADER;
 use crate::control::GatewayControlDecision;
+use crate::executor::{maybe_execute_stream_request, maybe_execute_sync_request};
 use crate::{AppState, GatewayError};
 
 use super::resolve_execution_runtime_auth_context;
@@ -38,23 +39,11 @@ pub(crate) async fn maybe_execute_via_control(
     }
 
     let response = if require_stream {
-        crate::execution_runtime::maybe_execute_via_execution_runtime_stream(
-            state,
-            parts,
-            &body_bytes,
-            trace_id,
-            Some(&local_decision),
-        )
-        .await?
+        maybe_execute_stream_request(state, parts, &body_bytes, trace_id, Some(&local_decision))
+            .await?
     } else {
-        crate::execution_runtime::maybe_execute_via_execution_runtime_sync(
-            state,
-            parts,
-            &body_bytes,
-            trace_id,
-            Some(&local_decision),
-        )
-        .await?
+        maybe_execute_sync_request(state, parts, &body_bytes, trace_id, Some(&local_decision))
+            .await?
     };
 
     Ok(response.map(mark_control_executed))