feat(saas): Phase 3 桌面端 SaaS 集成 — 客户端、Store、UI、LLM 适配器

- saas-client.ts: SaaS HTTP 客户端 (登录/注册/Token/模型列表/Chat Relay/配置同步)
- saasStore.ts: Zustand 状态管理 (登录态、连接模式、可用模型、localStorage 持久化)
- connectionStore.ts: 集成 SaaS 模式分支 (connect() 优先检查 SaaS 连接模式)
- llm-service.ts: SaasLLMAdapter 实现 (通过 SaaS Relay 代理 LLM 调用)
- SaaSLogin.tsx: 登录/注册表单 (服务器地址、用户名、密码、邮箱)
- SaaSStatus.tsx: 连接状态展示 (账号信息、健康检查、可用模型列表)
- SaaSSettings.tsx: SaaS 设置页面入口 (登录态切换、功能列表)
- SettingsLayout.tsx: 添加 SaaS 平台菜单项
- store/index.ts: 导出 useSaaSStore

desktop/src/store/index.ts

@@ -35,6 +35,10 @@ export type { SessionStore, SessionStateSlice, SessionActionsSlice, Session, Ses
 export { useMemoryGraphStore } from './memoryGraphStore';
 export type { MemoryGraphStore, GraphNode, GraphEdge, GraphFilter, GraphLayout } from './memoryGraphStore';
 
+// === SaaS Store ===
+export { useSaaSStore } from './saasStore';
+export type { SaaSStore, SaaSStateSlice, SaaSActionsSlice, ConnectionMode } from './saasStore';
+
 
 // === Browser Hand Store ===
 export { useBrowserHandStore } from './browserHandStore';