fix: 修复4个已知BUG — P1 ChatList/P2 错误密码/P3 Copilot崩溃/P3超管entrypoint

P1: ChatList.vue — 添加 conversationStats watch fallback，检测 stats>0
   但 chatList 为空时自动触发 fetchConversations
P2: api.js parseAPIErrorResponse — 处理 error 字段为对象时提取 .message
P3: CopilotContainer.vue — activeAssistant 判空保护
P3: 新建 super_admin.html + vite.config.ts rewrite 规则
    (注：entrypoint 仅含样式，Vue应用代码待补)
防御: NotificationTable.vue — 可选链保护 primary_actor.meta 路径

frontend/app/javascript/dashboard/components/copilot/CopilotContainer.vue

@@ -66,7 +66,10 @@ const activeAssistant = computed(() => {
     if (inboxMatchedAssistant) return inboxMatchedAssistant;
   }
   // If neither of the above is available, the first assistant in the account takes preference.
-  return assistants.value[0];
+  if (assistants.value && assistants.value.length > 0) {
+    return assistants.value[0];
+  }
+  return null;
 });
 
 const closeCopilotPanel = () => {