refactor: 大规模模块拆分与重组，新增 aether-admin crate

- 新建独立 aether-admin crate 承载 admin 相关共享契约与纯辅助函数
- 拆分 ai_pipeline 下 kiro/private_envelope/conversion/planner 等大文件为子模块目录
- 重组 admin handlers 各业务域（billing/oauth/provider/system/users 等）为目录结构，移除 shared.rs/builders.rs 等反模式
- 移除 ai_pipeline runtime adapters 旧实现（claude/openai/gemini/kiro/vertex/antigravity 等），改由 provider transport 统一承载
- 移除 control_facade/execution_facade/auth_snapshot_facade 等冗余 facade 层
- 拆分 query/billing 与 query/monitoring 模块、state/runtime/payments 与 security 模块
- 扩展架构测试覆盖 admin_billing/admin_model/admin_users 等新模块
- 删除 docs/architecture/refactor-execution-plan.md 已完成的执行计划文档

apps/aether-gateway/src/async_task/mod.rs

@@ -11,7 +11,8 @@ pub(crate) use http::{
 };
 pub(crate) use query::{
     read_video_task_detail, read_video_task_page, read_video_task_stats,
-    read_video_task_video_source,
+    read_video_task_video_source, VideoTaskPageResponse, VideoTaskStatsResponse,
+    VideoTaskVideoSource,
 };
 pub(crate) use runtime::{
     execute_video_task_refresh_plan, finalize_video_task_if_terminal, spawn_video_task_poller,

apps/aether-gateway/src/async_task/runtime.rs

@@ -11,7 +11,7 @@ use tokio::task::JoinHandle;
 use tracing::{info, warn};
 
 use crate::log_ids::short_request_id;
-use crate::usage::event::{UsageEvent, UsageEventData, UsageEventType};
+use crate::usage::{UsageEvent, UsageEventData, UsageEventType};
 use crate::video_tasks::{LocalVideoTaskReadRefreshPlan, LocalVideoTaskSnapshot};
 use crate::{AppState, GatewayError};