perf: 优化路由守卫安装检查，使用 localStorage 缓存

- 将安装状态缓存到 localStorage，有效期 24 小时
- 避免每次路由切换都发起 HTTP 请求
- 显著提升页面切换速度

frontend/src/router/guard/index.ts

@@ -1,25 +1,52 @@
 import type { Router } from 'vue-router'
 
-let installChecked = false
-let isInstalled = false
+const INSTALL_CACHE_KEY = 'app_installed'
+const INSTALL_CACHE_EXPIRY = 24 * 60 * 60 * 1000
+
+function getCachedInstallStatus(): boolean | null {
+  try {
+    const cached = localStorage.getItem(INSTALL_CACHE_KEY)
+    if (cached) {
+      const { installed, timestamp } = JSON.parse(cached)
+      if (Date.now() - timestamp < INSTALL_CACHE_EXPIRY) {
+        return installed
+      }
+    }
+  }
+  catch {
+    return null
+  }
+  return null
+}
+
+function setCachedInstallStatus(installed: boolean) {
+  try {
+    localStorage.setItem(INSTALL_CACHE_KEY, JSON.stringify({
+      installed,
+      timestamp: Date.now(),
+    }))
+  }
+  catch {
+  }
+}
 
 export function resetInstallCheck() {
-  installChecked = false
-  isInstalled = false
+  localStorage.removeItem(INSTALL_CACHE_KEY)
 }
 
 async function checkInstallStatus(): Promise<boolean> {
-  if (installChecked) return isInstalled
+  const cached = getCachedInstallStatus()
+  if (cached !== null) return cached
+
   try {
     const res = await fetch('/api/install/status')
     const data = await res.json()
-    isInstalled = data?.data?.installed ?? false
-    installChecked = true
-    return isInstalled
+    const installed = data?.data?.installed ?? false
+    setCachedInstallStatus(installed)
+    return installed
   }
   catch {
-    installChecked = true
-    isInstalled = false
+    setCachedInstallStatus(false)
     return false
   }
 }