fix: harden cloud storage security

backend/fix_expires_at_format.js

@@ -19,8 +19,20 @@ shares.forEach(share => {
   
   // 如果是ISO格式(包含T和Z),需要转换
   if (oldFormat.includes('T') || oldFormat.includes('Z')) {
-    // 转换为 SQLite datetime 格式: YYYY-MM-DD HH:MM:SS
-    const newFormat = oldFormat.replace('T', ' ').replace(/\.\d+Z$/, '');
+    const parsed = new Date(oldFormat);
+    if (Number.isNaN(parsed.getTime())) {
+      console.warn(`跳过无法解析的时间: ${share.share_code} -> ${oldFormat}`);
+      return;
+    }
+
+    // 转换为本地时区 SQLite datetime 格式: YYYY-MM-DD HH:MM:SS
+    const year = parsed.getFullYear();
+    const month = String(parsed.getMonth() + 1).padStart(2, '0');
+    const day = String(parsed.getDate()).padStart(2, '0');
+    const hours = String(parsed.getHours()).padStart(2, '0');
+    const minutes = String(parsed.getMinutes()).padStart(2, '0');
+    const seconds = String(parsed.getSeconds()).padStart(2, '0');
+    const newFormat = `${year}-${month}-${day} ${hours}:${minutes}:${seconds}`;
     
     updateStmt.run(newFormat, share.id);
     fixed++;