fix(desktop): 替换 require() 为 ES import — 修复生产构建崩溃

- connectionStore: 2 处 require() → loadConversationStore() 异步预加载 + 闭包引用
- saasStore: 1 处 require() → await import()（logout 是 async）
- llm-service: 1 处 require() → 顶层 import（无循环依赖）
- streamStore: 移除重复动态导入，统一使用顶层 useConnectionStore
- tsc --noEmit 0 errors

desktop/src/store/chat/streamStore.ts

@@ -57,7 +57,6 @@ async function tryRecoverFromAuthError(error: string): Promise<string | null> {
     const newToken = await saasClient.refreshMutex();
     if (newToken) {
       // Update kernel config with refreshed token → triggers kernel re-init via changed api_key detection
-      const { useConnectionStore } = await import('../connectionStore');
       const { getKernelClient } = await import('../../lib/kernel-client');
       const kernelClient = getKernelClient();
       const currentConfig = kernelClient.getConfig();