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/maintenance/runtime/tests.rs

@@ -275,20 +275,18 @@ fn usage_cleanup_window_uses_non_overlapping_ranges() {
 
 #[tokio::test]
 async fn summarize_postgres_pool_uses_busy_connections_for_usage_rate() {
-    let data = GatewayDataState::from_config(
-        crate::data::GatewayDataConfig::from_postgres_config(
-            aether_data::postgres::PostgresPoolConfig {
-                database_url: "postgres://localhost/aether".to_string(),
-                min_connections: 1,
-                max_connections: 8,
-                acquire_timeout_ms: 1_000,
-                idle_timeout_ms: 5_000,
-                max_lifetime_ms: 30_000,
-                statement_cache_capacity: 64,
-                require_ssl: false,
-            },
-        ),
-    )
+    let data = GatewayDataState::from_config(crate::data::GatewayDataConfig::from_postgres_config(
+        aether_data::postgres::PostgresPoolConfig {
+            database_url: "postgres://localhost/aether".to_string(),
+            min_connections: 1,
+            max_connections: 8,
+            acquire_timeout_ms: 1_000,
+            idle_timeout_ms: 5_000,
+            max_lifetime_ms: 30_000,
+            statement_cache_capacity: 64,
+            require_ssl: false,
+        },
+    ))
     .expect("gateway data state should build");
 
     let summary = summarize_postgres_pool(&data).expect("pool summary should exist");