feat: 文传易匿名临时文件传输站初始版本

- 后端 .NET 8 + FreeSql + 阿里云 OSS，支持共享/私密/标签三种文件模式
- 前端 Vue3 + Vite + TDesign，上传/取件/管理三页
- 取件码/二维码/海报合成（含保存二维码为图片）
- deploy/ 部署文档与一键 FTP 发布脚本
- appsettings.json 含真实凭据，已 gitignore 不入库

backend/WenChuanyi.Api/Services/ExpiredFileCleanerService.cs

@@ -0,0 +1,67 @@
+using WenChuanyi.Api.Models;
+
+namespace WenChuanyi.Api.Services;
+
+/// <summary>过期文件定时清理：每 N 分钟扫描 IsPermanent=false 且已过期的记录，先删记录再删 OSS 对象</summary>
+public class ExpiredFileCleanerService : BackgroundService
+{
+    private readonly IServiceScopeFactory _scopeFactory;
+    private readonly ILogger<ExpiredFileCleanerService> _logger;
+    private readonly TimeSpan _interval;
+
+    public ExpiredFileCleanerService(
+        IServiceScopeFactory scopeFactory,
+        IConfiguration cfg,
+        ILogger<ExpiredFileCleanerService> logger)
+    {
+        _scopeFactory = scopeFactory;
+        _logger = logger;
+        var minutes = cfg.GetValue<int>("Cleaner:IntervalMinutes", 30);
+        _interval = TimeSpan.FromMinutes(Math.Max(1, minutes));
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("过期文件清理任务启动，间隔 {Minutes} 分钟", _interval.TotalMinutes);
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await CleanExpiredAsync(stoppingToken);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "过期文件清理任务异常");
+            }
+            await Task.Delay(_interval, stoppingToken);
+        }
+    }
+
+    private async Task CleanExpiredAsync(CancellationToken ct)
+    {
+        await using var scope = _scopeFactory.CreateAsyncScope();
+        var fsql = scope.ServiceProvider.GetRequiredService<IFreeSql>();
+        var oss = scope.ServiceProvider.GetRequiredService<OssStorageService>();
+
+        var expired = await fsql.Select<FileItem>()
+            .Where(f => !f.IsPermanent && f.ExpiresAt != null && f.ExpiresAt < DateTime.Now)
+            .ToListAsync(ct);
+
+        if (expired.Count == 0)
+        {
+            return;
+        }
+
+        _logger.LogInformation("发现 {Count} 个过期文件，开始清理", expired.Count);
+        foreach (var item in expired)
+        {
+            // 先删数据库记录
+            var deleted = await fsql.Delete<FileItem>().Where(f => f.Id == item.Id).ExecuteAffrowsAsync(ct) > 0;
+            // 再删 OSS 对象（失败仅记日志，不阻塞任务）
+            if (deleted)
+            {
+                oss.TryDeleteObject(item.ObjectKey);
+            }
+        }
+    }
+}