fix: 多选同步弹窗复用站点同步表单缓存

- 抽取站点地址与 Token 的 24 小时缓存工具
- 存储页与多选同步弹窗共用 pichost.site-sync-form
- 弹窗打开时读取最新缓存，修改后写回
- 增加缓存读取与过期测试

app/utils/site-sync-form.ts

@@ -0,0 +1,52 @@
+export const SITE_SYNC_FORM_STORAGE_KEY = 'pichost.site-sync-form'
+export const SITE_SYNC_FORM_TTL_MS = 24 * 60 * 60 * 1000
+
+export interface SiteSyncFormCache {
+  targetBaseUrl: string
+  token: string
+}
+
+function getStorage(): Storage | null {
+  return typeof localStorage === 'undefined' ? null : localStorage
+}
+
+export function loadSiteSyncForm(): SiteSyncFormCache | null {
+  const storage = getStorage()
+  if (!storage) return null
+
+  try {
+    const raw = storage.getItem(SITE_SYNC_FORM_STORAGE_KEY)
+    if (!raw) return null
+    const data = JSON.parse(raw) as {
+      targetBaseUrl?: unknown
+      token?: unknown
+      savedAt?: unknown
+    }
+    if (typeof data.savedAt !== 'number' || Date.now() - data.savedAt > SITE_SYNC_FORM_TTL_MS) {
+      storage.removeItem(SITE_SYNC_FORM_STORAGE_KEY)
+      return null
+    }
+    return {
+      targetBaseUrl: typeof data.targetBaseUrl === 'string' ? data.targetBaseUrl : '',
+      token: typeof data.token === 'string' ? data.token : ''
+    }
+  } catch {
+    storage.removeItem(SITE_SYNC_FORM_STORAGE_KEY)
+    return null
+  }
+}
+
+export function saveSiteSyncForm(targetBaseUrl: string, token: string): void {
+  const storage = getStorage()
+  if (!storage) return
+
+  try {
+    storage.setItem(SITE_SYNC_FORM_STORAGE_KEY, JSON.stringify({
+      targetBaseUrl,
+      token,
+      savedAt: Date.now()
+    }))
+  } catch {
+    // 存储不可用时忽略
+  }
+}