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-EFCore/Database/AppDataContext.cs

@@ -25,6 +25,8 @@ namespace FileShare_EFCore.Database
         /// <summary>文件库文件记录数据</summary>
         public DbSet<ManagedFileRecord> ManagedFileRecords => Set<ManagedFileRecord>();
 
+        public DbSet<ManagedThumbnailMap> ManagedThumbnailMaps => Set<ManagedThumbnailMap>();
+
         /// <summary>
         /// 配置实体映射，包括主键、索引和属性约束。
         /// </summary>
@@ -66,8 +68,10 @@ namespace FileShare_EFCore.Database
             {
                 entity.HasKey(e => e.Id).HasName("pk-managed-file-record");
                 entity.HasIndex(e => e.LibraryRootId).HasDatabaseName("idx-managed-file-record-root-id");
+                entity.HasIndex(e => e.ThumbnailId).HasDatabaseName("idx-managed-file-record-thumbnail-id");
                 entity.HasIndex(e => e.AbsolutePath).IsUnique().HasDatabaseName("idx-managed-file-record-absolute-path");
                 entity.HasIndex(e => new { e.MediaType, e.Exists }).HasDatabaseName("idx-managed-file-record-media-type-exists");
+                entity.HasIndex(e => e.LastPlayedAt).HasDatabaseName("idx-managed-file-record-last-played-at");
                 entity.Property(e => e.FileName).HasMaxLength(260);
                 entity.Property(e => e.RelativePath).HasMaxLength(1024);
                 entity.Property(e => e.AbsolutePath).HasMaxLength(2048);
@@ -78,6 +82,23 @@ namespace FileShare_EFCore.Database
                     .WithMany(e => e.Files)
                     .HasForeignKey(e => e.LibraryRootId)
                     .OnDelete(DeleteBehavior.Cascade);
+                entity.HasOne(e => e.Thumbnail)
+                    .WithMany(e => e.Files)
+                    .HasForeignKey(e => e.ThumbnailId)
+                    .OnDelete(DeleteBehavior.SetNull);
+            });
+
+            modelBuilder.Entity<ManagedThumbnailMap>(entity =>
+            {
+                entity.HasKey(e => e.Id).HasName("pk-managed-thumbnail-map");
+                entity.HasIndex(e => e.LibraryRootId).HasDatabaseName("idx-managed-thumbnail-map-root-id");
+                entity.HasIndex(e => e.RelativePath).IsUnique().HasDatabaseName("idx-managed-thumbnail-map-relative-path");
+                entity.Property(e => e.RelativePath).HasMaxLength(1024);
+                entity.Property(e => e.ContentType).HasMaxLength(100);
+                entity.HasOne(e => e.LibraryRoot)
+                    .WithMany(e => e.Thumbnails)
+                    .HasForeignKey(e => e.LibraryRootId)
+                    .OnDelete(DeleteBehavior.Cascade);
             });
         }
     }