feat: 新增可配置的文件库扫描日志记录及缩略图清理功能

- 为文件库的定时轮询及根目录扫描过程，新增扫描生​​命周期日志
- 允许通过 `appsettings` 配置文件，自定义定时扫描的轮询间隔
- 当检测到媒体文件已被删除时，自动清理过期的缩略图映射记录及对应的缩略图文件

FileShare-Services/Services/FileLibrary/FileLibraryService.cs

@@ -129,10 +129,14 @@ namespace FileShare_Services.Services.FileLibrary
             var root = await db.ManagedLibraryRoots.FirstOrDefaultAsync(item => item.Id == rootId, cancellationToken)
                 ?? throw new InvalidOperationException("文件库目录不存在。");
 
+            Serilog.Log.Information("开始扫描文件库根目录 RootId={RootId} Path={Path}", root.Id, root.Path);
             root.LastScanStartedAt = DateTime.UtcNow;
             root.LastScanError = null;
             await db.SaveChangesAsync(cancellationToken);
 
+            var staleFileCount = 0;
+            var staleThumbnailPaths = new List<string>();
+
             try
             {
                 if (!Directory.Exists(root.Path))
@@ -200,13 +204,48 @@ namespace FileShare_Services.Services.FileLibrary
                     }
                 }
 
-                foreach (var stale in existing.Values.Where(file => !seen.Contains(file.AbsolutePath)))
+                var staleFiles = existing.Values
+                    .Where(file => !seen.Contains(file.AbsolutePath))
+                    .ToList();
+                staleFileCount = staleFiles.Count;
+
+                foreach (var stale in staleFiles)
                 {
                     stale.Exists = false;
                 }
 
+                var activeThumbnailIds = existing.Values
+                    .Where(file => file.Exists && file.ThumbnailId is not null)
+                    .Select(file => file.ThumbnailId!.Value)
+                    .ToHashSet();
+                var staleThumbnailIds = staleFiles
+                    .Where(file => file.ThumbnailId is not null && !activeThumbnailIds.Contains(file.ThumbnailId.Value))
+                    .Select(file => file.ThumbnailId!.Value)
+                    .Distinct()
+                    .ToList();
+
+                if (staleThumbnailIds.Count > 0)
+                {
+                    var staleThumbnails = await db.ManagedThumbnailMaps
+                        .Where(thumbnail => thumbnail.LibraryRootId == root.Id && staleThumbnailIds.Contains(thumbnail.Id))
+                        .ToListAsync(cancellationToken);
+
+                    staleThumbnailPaths = staleThumbnails
+                        .Select(thumbnail => thumbnail.RelativePath)
+                        .ToList();
+
+                    foreach (var stale in staleFiles.Where(file => file.ThumbnailId is not null && staleThumbnailIds.Contains(file.ThumbnailId.Value)))
+                    {
+                        stale.ThumbnailId = null;
+                        stale.Thumbnail = null;
+                    }
+
+                    db.ManagedThumbnailMaps.RemoveRange(staleThumbnails);
+                }
+
                 root.LastScanCompletedAt = DateTime.UtcNow;
                 await db.SaveChangesAsync(cancellationToken);
+                DeleteThumbnailFiles(staleThumbnailPaths);
             }
             catch (Exception ex)
             {
@@ -219,6 +258,12 @@ namespace FileShare_Services.Services.FileLibrary
             }
 
             var count = await db.ManagedFileRecords.CountAsync(file => file.LibraryRootId == root.Id && file.Exists, cancellationToken);
+            Serilog.Log.Information(
+                "扫描文件库根目录完成 RootId={RootId} FileCount={FileCount} StaleFiles={StaleFiles} RemovedThumbnails={RemovedThumbnails}",
+                root.Id,
+                count,
+                staleFileCount,
+                staleThumbnailPaths.Count);
             return ToRootDto(root, count);
         }
 
@@ -229,19 +274,29 @@ namespace FileShare_Services.Services.FileLibrary
             var roots = await db.ManagedLibraryRoots
                 .Where(root => root.IsEnabled && root.IsAvailable)
                 .ToListAsync(cancellationToken);
-
-            foreach (var root in roots)
-            {
-                var interval = Math.Max(1, root.ScanIntervalMinutes);
-                var isDue = root.LastScanCompletedAt is null || root.LastScanCompletedAt.Value.AddMinutes(interval) <= now;
-                if (!isDue)
+            var dueRoots = roots
+                .Where(root =>
                 {
-                    continue;
-                }
+                    var interval = Math.Max(1, root.ScanIntervalMinutes);
+                    return root.LastScanCompletedAt is null || root.LastScanCompletedAt.Value.AddMinutes(interval) <= now;
+                })
+                .ToList();
 
+            Serilog.Log.Information(
+                "文件库定时扫描检查完成 CheckedRoots={CheckedRoots} DueRoots={DueRoots}",
+                roots.Count,
+                dueRoots.Count);
+
+            foreach (var root in dueRoots)
+            {
                 try
                 {
-                    await ScanRootAsync(root.Id, cancellationToken);
+                    Serilog.Log.Information("文件库定时扫描开始 RootId={RootId} Path={Path}", root.Id, root.Path);
+                    var scannedRoot = await ScanRootAsync(root.Id, cancellationToken);
+                    Serilog.Log.Information(
+                        "文件库定时扫描完成 RootId={RootId} FileCount={FileCount}",
+                        scannedRoot.Id,
+                        scannedRoot.FileCount);
                 }
                 catch (Exception ex)
                 {
@@ -498,6 +553,29 @@ namespace FileShare_Services.Services.FileLibrary
             return string.IsNullOrWhiteSpace(directory.Name) ? directory.FullName : directory.Name;
         }
 
+        /// <summary>
+        /// 删除数据库中已释放的缩略图文件，失败时保留扫描结果并记录告警。
+        /// </summary>
+        /// <param name="relativePaths">待删除缩略图相对路径。</param>
+        private void DeleteThumbnailFiles(IEnumerable<string> relativePaths)
+        {
+            foreach (var relativePath in relativePaths)
+            {
+                try
+                {
+                    var absolutePath = thumbnailService.GetAbsolutePath(relativePath);
+                    if (File.Exists(absolutePath))
+                    {
+                        File.Delete(absolutePath);
+                    }
+                }
+                catch (Exception ex)
+                {
+                    Serilog.Log.Warning(ex, "清理失效缩略图文件失败 ThumbnailPath={ThumbnailPath}", relativePath);
+                }
+            }
+        }
+
         /// <summary>
         /// 规范化扫描间隔，限制在 1 到 1440 分钟范围内，未指定时使用默认值。
         /// </summary>