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-model-fetch/Cargo.toml

@@ -7,7 +7,7 @@ repository.workspace = true
 
 [dependencies]
 aether-contracts.workspace = true
-aether-data.workspace = true
+aether-data-contracts.workspace = true
 aether-provider-transport.workspace = true
 aether-scheduler-core.workspace = true
 async-trait.workspace = true

crates/aether-model-fetch/src/association_sync.rs

@@ -1,10 +1,10 @@
 use std::collections::BTreeSet;
 
-use aether_data::repository::global_models::{
+use aether_data_contracts::repository::global_models::{
     AdminGlobalModelListQuery, AdminProviderModelListQuery, StoredAdminGlobalModelPage,
     StoredAdminProviderModel, UpsertAdminProviderModelRecord,
 };
-use aether_data::repository::provider_catalog::StoredProviderCatalogKey;
+use aether_data_contracts::repository::provider_catalog::StoredProviderCatalogKey;
 use aether_scheduler_core::matches_model_mapping;
 use async_trait::async_trait;
 use serde_json::Value;

crates/aether-model-fetch/src/logic.rs

@@ -1,6 +1,6 @@
 use std::collections::{BTreeMap, BTreeSet};
 
-use aether_data::repository::provider_catalog::{
+use aether_data_contracts::repository::provider_catalog::{
     StoredProviderCatalogEndpoint, StoredProviderCatalogKey,
 };
 use aether_provider_transport::provider_types::provider_type_supports_model_fetch;
@@ -360,7 +360,7 @@ fn normalize_api_format(value: &str) -> String {
 
 #[cfg(test)]
 mod tests {
-    use aether_data::repository::provider_catalog::{
+    use aether_data_contracts::repository::provider_catalog::{
         StoredProviderCatalogEndpoint, StoredProviderCatalogKey,
     };
     use serde_json::json;