fix: 修复前端多个 bug

1. 版本号闪烁问题
   - 将版本信息缓存到 Pinia store，避免每次路由切换都重新请求
   - 添加加载占位符，版本为空时显示骨架屏

2. 管理员登录跳转问题
   - 管理员登录后现在正确跳转到 /admin/dashboard
   - 普通用户仍跳转到 /dashboard

3. Dashboard 页面空白报错
   - 修复 API 返回 null 时访问 .length 导致的 TypeError
   - 为 computed 属性添加可选链操作符保护
   - 为数据赋值添加空数组默认值

frontend/src/stores/app.ts

@@ -6,14 +6,24 @@
 import { defineStore } from 'pinia';
 import { ref, computed } from 'vue';
 import type { Toast, ToastType } from '@/types';
+import { checkUpdates as checkUpdatesAPI, type VersionInfo, type ReleaseInfo } from '@/api/admin/system';
 
 export const useAppStore = defineStore('app', () => {
   // ==================== State ====================
-  
+
   const sidebarCollapsed = ref<boolean>(false);
   const loading = ref<boolean>(false);
   const toasts = ref<Toast[]>([]);
 
+  // Version cache state
+  const versionLoaded = ref<boolean>(false);
+  const versionLoading = ref<boolean>(false);
+  const currentVersion = ref<string>('');
+  const latestVersion = ref<string>('');
+  const hasUpdate = ref<boolean>(false);
+  const buildType = ref<string>('source');
+  const releaseInfo = ref<ReleaseInfo | null>(null);
+
   // Auto-incrementing ID for toasts
   let toastIdCounter = 0;
 
@@ -192,6 +202,56 @@ export const useAppStore = defineStore('app', () => {
     toasts.value = [];
   }
 
+  // ==================== Version Management ====================
+
+  /**
+   * Fetch version info (uses cache unless force=true)
+   * @param force - Force refresh from API
+   */
+  async function fetchVersion(force = false): Promise<VersionInfo | null> {
+    // Return cached data if available and not forcing refresh
+    if (versionLoaded.value && !force) {
+      return {
+        current_version: currentVersion.value,
+        latest_version: latestVersion.value,
+        has_update: hasUpdate.value,
+        build_type: buildType.value,
+        release_info: releaseInfo.value || undefined,
+        cached: true,
+      };
+    }
+
+    // Prevent duplicate requests
+    if (versionLoading.value) {
+      return null;
+    }
+
+    versionLoading.value = true;
+    try {
+      const data = await checkUpdatesAPI(force);
+      currentVersion.value = data.current_version;
+      latestVersion.value = data.latest_version;
+      hasUpdate.value = data.has_update;
+      buildType.value = data.build_type || 'source';
+      releaseInfo.value = data.release_info || null;
+      versionLoaded.value = true;
+      return data;
+    } catch (error) {
+      console.error('Failed to fetch version:', error);
+      return null;
+    } finally {
+      versionLoading.value = false;
+    }
+  }
+
+  /**
+   * Clear version cache (e.g., after update)
+   */
+  function clearVersionCache(): void {
+    versionLoaded.value = false;
+    hasUpdate.value = false;
+  }
+
   // ==================== Return Store API ====================
 
   return {
@@ -199,10 +259,19 @@ export const useAppStore = defineStore('app', () => {
     sidebarCollapsed,
     loading,
     toasts,
-    
+
+    // Version state
+    versionLoaded,
+    versionLoading,
+    currentVersion,
+    latestVersion,
+    hasUpdate,
+    buildType,
+    releaseInfo,
+
     // Computed
     hasActiveToasts,
-    
+
     // Actions
     toggleSidebar,
     setSidebarCollapsed,
@@ -217,5 +286,9 @@ export const useAppStore = defineStore('app', () => {
     withLoading,
     withLoadingAndError,
     reset,
+
+    // Version actions
+    fetchVersion,
+    clearVersionCache,
   };
 });