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

crates/aether-video-tasks-core/src/gemini.rs

@@ -1,5 +1,7 @@
 use aether_contracts::{ExecutionPlan, RequestBody};
-use aether_data::repository::video_tasks::{StoredVideoTask, UpsertVideoTask, VideoTaskStatus};
+use aether_data_contracts::repository::video_tasks::{
+    StoredVideoTask, UpsertVideoTask, VideoTaskStatus,
+};
 use serde_json::{json, Map, Value};
 
 use crate::{
@@ -362,7 +364,7 @@ impl GeminiVideoTaskSeed {
 
 #[cfg(test)]
 mod tests {
-    use aether_data::repository::video_tasks::{StoredVideoTask, VideoTaskStatus};
+    use aether_data_contracts::repository::video_tasks::{StoredVideoTask, VideoTaskStatus};
 
     use super::map_gemini_stored_task_to_read_response;