feat: 微服务架构拆分和前后端优化

后端:
- 拆分出 agent_service, runtime_service, trading_service, news_service
- Gateway 模块化拆分 (gateway_*.py)
- 添加 domains/ 领域层
- 新增 control_client, runtime_client
- 更新 start-dev.sh 支持 split 服务模式

前端:
- 完善 API 服务层 (newsApi, tradingApi)
- 更新 vite.config.js
- Explain 组件优化

测试:
- 添加多个服务 app 测试

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/compat-removal-plan.md

@@ -0,0 +1,28 @@
+# Compatibility Removal Plan
+
+This document tracks the remaining migration-only surfaces that still exist
+after the move to split-first development.
+
+## Migration-only Surfaces
+
+None currently remain as dedicated compatibility wrappers.
+
+## Completed Removals
+
+### `backend.app`
+
+- Removed after compatibility startup switched to
+  `backend.apps.combined_service:app` directly.
+
+### `shared.client.AgentServiceClient`
+
+- Removed after split-aware clients became the default import surface.
+- Replacement:
+  - `ControlPlaneClient`
+  - `RuntimeServiceClient`
+  - `TradingServiceClient`
+  - `NewsServiceClient`
+
+### `backend.apps.combined_service`
+
+- Removed after split-service mode became the only supported dev startup path.