fix(ui): 5 项 E2E 测试 Bug 修复 — Agent 502 / 错误持久化 / 模型标记 / 侧面板 / 记忆页

- BUG-01: createFromTemplate 在 saas-relay 模式下 try-catch 跳过本地 Kernel
- BUG-02: upsertActiveConversation 持久化前剥离 error/streaming/optimistic 字段
- BUG-04: ModelSelector 添加 available 标记，ChatArea 追踪失败模型 ID
- BUG-05: VikingPanel 移除 status?.available 门控，不可用时 disabled + 重连按钮
- BUG-06: 侧面板 tooltip 改为"查看产物文件"，空状态增加图标和说明

desktop/src/store/chat/conversationStore.ts

@@ -326,8 +326,16 @@ export const useConversationStore = create<ConversationState>()(
   upsertActiveConversation: (currentMessages: ChatMessage[]) => {
     const state = get();
     const currentId = state.currentConversationId || null;
+    // Strip transient fields (error, streaming, optimistic) before persistence
+    // so old errors don't permanently show "重试" buttons on reload
+    const cleanMessages = currentMessages.map(m => ({
+      ...m,
+      error: undefined,
+      streaming: undefined,
+      optimistic: undefined,
+    }));
     const conversations = upsertActiveConversation(
-      [...state.conversations], currentMessages, state.sessionKey,
+      [...state.conversations], cleanMessages, state.sessionKey,
       state.currentConversationId, state.currentAgent,
     );
     // If this was a new conversation (no prior currentConversationId),