feat: 视频缩略图生成、最近文件面板与前端视图重构

- 新增 VideoThumbnailService，基于 ffmpeg 截取视频缩略图，ffprobe 提取时长
  - 新增 ManagedThumbnailMap 模型及多数据库迁移，存储缩略图元数据
  - 新增 /api/thumbnails/{id} 缩略图流端点
  - 新增最近添加/最近播放 API 与前端面板，支持列表/网格双视图切换
  - FileRecordDto 扩展 thumbnailUrl、videoDuration、lastPlayedAt 字段
  - 前端新增文件库 Tab 导航、卡片网格视图、视频海报与时长信息栏
  - 添加文件库目录不再同步全量扫描，改为后台异步自动扫描

FileShare-Services/Services/FileLibrary/FileLibraryService.cs

@@ -10,7 +10,7 @@ namespace FileShare_Services.Services.FileLibrary
     /// <summary>
     /// 文件库核心业务服务，实现磁盘枚举、目录管理、文件扫描与检索。
     /// </summary>
-    public sealed class FileLibraryService(AppDataContext db) : IFileLibraryService
+    public sealed class FileLibraryService(AppDataContext db, IVideoThumbnailService thumbnailService) : IFileLibraryService
     {
         /// <summary>
         /// 默认扫描间隔（分钟），当请求未指定间隔时使用。
@@ -80,7 +80,9 @@ namespace FileShare_Services.Services.FileLibrary
                 existing.DisplayName = ResolveDisplayName(normalized, request.DisplayName);
                 existing.ScanIntervalMinutes = NormalizeInterval(request.ScanIntervalMinutes);
                 await db.SaveChangesAsync(cancellationToken);
-                return await ScanRootAsync(existing.Id, cancellationToken);
+                var existingCount = await db.ManagedFileRecords
+                    .CountAsync(file => file.LibraryRootId == existing.Id && file.Exists, cancellationToken);
+                return ToRootDto(existing, existingCount);
             }
 
             var root = new ManagedLibraryRoot
@@ -95,7 +97,7 @@ namespace FileShare_Services.Services.FileLibrary
             db.ManagedLibraryRoots.Add(root);
             await db.SaveChangesAsync(cancellationToken);
 
-            return await ScanRootAsync(root.Id, cancellationToken);
+            return ToRootDto(root, 0);
         }
 
         /// <inheritdoc />
@@ -178,6 +180,24 @@ namespace FileShare_Services.Services.FileLibrary
                     record.ContentType = contentType;
                     record.Exists = true;
                     record.LastSeenAt = DateTime.UtcNow;
+
+                    if (mediaType == "video" && record.ThumbnailId is null)
+                    {
+                        var thumbnail = await thumbnailService.GenerateThumbnailAsync(root.Id, absolutePath, cancellationToken);
+                        if (thumbnail is not null)
+                        {
+                            var map = new ManagedThumbnailMap
+                            {
+                                LibraryRootId = root.Id,
+                                RelativePath = thumbnail.RelativePath,
+                                ContentType = thumbnail.ContentType,
+                            };
+                            db.ManagedThumbnailMaps.Add(map);
+                            record.Thumbnail = map;
+                        }
+
+                        record.VideoDuration ??= thumbnailService.GetVideoDuration(absolutePath);
+                    }
                 }
 
                 foreach (var stale in existing.Values.Where(file => !seen.Contains(file.AbsolutePath)))
@@ -356,6 +376,34 @@ namespace FileShare_Services.Services.FileLibrary
             return new TextPreviewDto(file.Id, file.FileName, content, stream.Length > MaxTextPreviewBytes);
         }
 
+        /// <inheritdoc />
+        public async Task<List<FileRecordDto>> GetRecentFilesAsync(string type, int count = 12, CancellationToken cancellationToken = default)
+        {
+            var query = db.ManagedFileRecords
+                .AsNoTracking()
+                .Where(file => file.Exists && file.LibraryRoot != null && file.LibraryRoot.IsAvailable);
+
+            query = type == "played"
+                ? query.Where(file => file.LastPlayedAt != null).OrderByDescending(file => file.LastPlayedAt)
+                : query.OrderByDescending(file => file.CreatedAt);
+
+            return await query
+                .Take(Math.Clamp(count, 1, 48))
+                .Select(file => ToFileDto(file))
+                .ToListAsync(cancellationToken);
+        }
+
+        /// <inheritdoc />
+        public async Task MarkFilePlayedAsync(int id, CancellationToken cancellationToken = default)
+        {
+            var record = await db.ManagedFileRecords.FindAsync([id], cancellationToken);
+            if (record is not null)
+            {
+                record.LastPlayedAt = DateTime.UtcNow;
+                await db.SaveChangesAsync(cancellationToken);
+            }
+        }
+
         /// <summary>
         /// 深度优先遍历目录树，枚举所有被 <see cref="MediaFileTypes"/> 支持的媒体文件路径。
         /// 遇到无权限的目录时跳过该分支继续遍历。
@@ -508,7 +556,10 @@ namespace FileShare_Services.Services.FileLibrary
                 file.ContentType,
                 $"/api/files/{file.Id}/stream",
                 file.MediaType == "text" ? $"/api/files/text?id={file.Id}" : null,
-                MediaFileTypes.IsBrowserPlayable(file.Extension));
+                MediaFileTypes.IsBrowserPlayable(file.Extension),
+                file.ThumbnailId is null ? null : $"/api/thumbnails/{file.ThumbnailId}",
+                file.VideoDuration,
+                file.LastPlayedAt);
         }
 
     }