docs: 为缩略图、最近文件相关新增类型补全中文 XML 文档注释

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

FileShare-Services/Services/FileLibrary/ThumbnailStreamService.cs

@@ -4,13 +4,26 @@ using Microsoft.EntityFrameworkCore;
 
 namespace FileShare_Services.Services.FileLibrary
 {
+    /// <summary>
+    /// 缩略图流服务接口，根据缩略图 ID 返回文件流响应。
+    /// </summary>
     public interface IThumbnailStreamService
     {
+        /// <summary>
+        /// 根据缩略图记录 ID 获取缩略图文件流响应。
+        /// </summary>
+        /// <param name="id">缩略图记录 ID。</param>
+        /// <param name="cancellationToken">取消令牌。</param>
+        /// <returns>文件流响应，不存在或文件丢失时返回 null。</returns>
         Task<FileStreamResponse?> GetThumbnailAsync(int id, CancellationToken cancellationToken = default);
     }
 
+    /// <summary>
+    /// 缩略图流服务实现，从数据库查找缩略图映射并返回对应的物理文件流。
+    /// </summary>
     public sealed class ThumbnailStreamService(AppDataContext db, IVideoThumbnailService thumbnails) : IThumbnailStreamService
     {
+        /// <inheritdoc />
         public async Task<FileStreamResponse?> GetThumbnailAsync(int id, CancellationToken cancellationToken = default)
         {
             var thumbnail = await db.ManagedThumbnailMaps