feat: 添加 OSS 存储配额功能

- 数据库：添加 oss_storage_quota 字段（0 表示无限制）
- 后端：登录/用户信息返回 OSS 配额
- 后端：管理员可设置用户 OSS 配额
- 后端：上传时检查 OSS 配额限制
- 前端：管理员编辑用户增加 OSS 配额设置
- 前端：用户文件页面显示 OSS 使用量和配额

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/server.js

@@ -1897,6 +1897,7 @@ app.post('/api/login',
           current_storage_type: user.current_storage_type || 'oss',
           local_storage_quota: user.local_storage_quota || 1073741824,
           local_storage_used: user.local_storage_used || 0,
+          oss_storage_quota: user.oss_storage_quota || 0, // 0 表示无限制
           // OSS配置来源（重要：用于前端判断是否使用OSS直连上传）
           oss_config_source: SettingsDB.hasUnifiedOssConfig() ? 'unified' : (user.has_oss_config ? 'personal' : 'none')
         }
@@ -2986,6 +2987,7 @@ app.get('/api/files/upload-signature', authMiddleware, async (req, res) => {
   const filename = req.query.filename;
   const uploadPath = req.query.path || '/'; // 上传目标路径
   const contentType = req.query.contentType || 'application/octet-stream';
+  const fileSize = parseInt(req.query.fileSize, 10) || 0;
 
   if (!filename) {
     return res.status(400).json({
@@ -3036,6 +3038,25 @@ app.get('/api/files/upload-signature', authMiddleware, async (req, res) => {
     });
   }
 
+  // OSS 配额检查（0 表示无限制）
+  const ossQuota = req.user.oss_storage_quota || 0;
+  if (ossQuota > 0 && fileSize > 0) {
+    // 获取当前 OSS 使用量
+    const { getOssUsage } = require('./storage');
+    try {
+      const ossUsage = await getOssUsage(req.user);
+      const currentUsed = ossUsage?.totalSize || 0;
+      if (currentUsed + fileSize > ossQuota) {
+        return res.status(400).json({
+          success: false,
+          message: 
+        });
+      }
+    } catch (usageErr) {
+      console.warn('[OSS配额检查] 获取使用量失败，跳过检查:', usageErr.message);
+    }
+  }
+
   try {
     const { S3Client, PutObjectCommand } = require('@aws-sdk/client-s3');
     const { getSignedUrl } = require('@aws-sdk/s3-request-presigner');
@@ -3169,6 +3190,25 @@ app.get('/api/files/download-url', authMiddleware, async (req, res) => {
     });
   }
 
+  // OSS 配额检查（0 表示无限制）
+  const ossQuota = req.user.oss_storage_quota || 0;
+  if (ossQuota > 0 && fileSize > 0) {
+    // 获取当前 OSS 使用量
+    const { getOssUsage } = require('./storage');
+    try {
+      const ossUsage = await getOssUsage(req.user);
+      const currentUsed = ossUsage?.totalSize || 0;
+      if (currentUsed + fileSize > ossQuota) {
+        return res.status(400).json({
+          success: false,
+          message: 
+        });
+      }
+    } catch (usageErr) {
+      console.warn('[OSS配额检查] 获取使用量失败，跳过检查:', usageErr.message);
+    }
+  }
+
   try {
     const { S3Client, GetObjectCommand } = require('@aws-sdk/client-s3');
     const { getSignedUrl } = require('@aws-sdk/s3-request-presigner');
@@ -5251,7 +5291,8 @@ app.get('/api/admin/users', authMiddleware, adminMiddleware, (req, res) => {
         storage_permission: u.storage_permission || 'oss_only',
         current_storage_type: u.current_storage_type || 'oss',
         local_storage_quota: u.local_storage_quota || 1073741824,
-        local_storage_used: u.local_storage_used || 0
+        local_storage_used: u.local_storage_used || 0,
+        oss_storage_quota: u.oss_storage_quota || 0
       }))
     });
   } catch (error) {
@@ -5847,7 +5888,7 @@ app.post('/api/admin/users/:id/storage-permission',
 
     try {
       const { id } = req.params;
-      const { storage_permission, local_storage_quota } = req.body;
+      const { storage_permission, local_storage_quota, oss_storage_quota } = req.body;
 
       // 参数验证：验证 ID 格式
       const userId = parseInt(id, 10);
@@ -5860,10 +5901,15 @@ app.post('/api/admin/users/:id/storage-permission',
 
       const updates = { storage_permission };
 
-      // 如果提供了配额，更新配额（单位：字节）
+      // 如果提供了本地配额，更新本地配额（单位：字节）
       if (local_storage_quota !== undefined) {
         updates.local_storage_quota = parseInt(local_storage_quota, 10);
       }
+      
+      // 如果提供了 OSS 配额，更新 OSS 配额（单位：字节，0 表示无限制）
+      if (oss_storage_quota !== undefined) {
+        updates.oss_storage_quota = parseInt(oss_storage_quota, 10);
+      }
 
       // 根据权限设置自动调整存储类型
       const user = UserDB.findById(userId);