feat: 前端组件拆分与文件库目录浏览功能

- 将 App.vue 拆分为 AdminPage、ClientPage、QrCodeModal 三个独立组件
- 新增 BrowseDirectory 接口，基于 RelativePath 实现层级目录浏览
- 前端新增面包屑导航、文件夹网格、文件列表等目录浏览 UI
- 新增对应 CSS 样式（breadcrumb、folder-grid、file-list 等）

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

Avalonia-Services/Services/FileLibrary/FileLibraryContracts.cs

@@ -69,6 +69,15 @@ namespace Avalonia_Services.Services.FileLibrary
         string? TextUrl,
         bool BrowserPlayable);
 
+    public sealed record BrowseDirectoryRequest(
+        [property: JsonPropertyName("rootId")] int RootId = 0,
+        [property: JsonPropertyName("path")] string? Path = null);
+
+    public sealed record BrowseDirectoryResponse(
+        string CurrentPath,
+        List<string> Subdirectories,
+        List<FileRecordDto> Files);
+
     public sealed record TextPreviewDto(
         int Id,
         string FileName,

Avalonia-Services/Services/FileLibrary/FileLibraryEndpointService.cs

@@ -64,6 +64,15 @@ namespace Avalonia_Services.Services.FileLibrary
                 : ResponseHelper.Ok(preview);
         }
 
+        public async Task<IApiResponse> BrowseDirectoryAsync(BrowseDirectoryRequest request)
+        {
+            if (request.RootId <= 0)
+                return ResponseHelper.Failure(400, "rootId 参数无效。");
+
+            var result = await fileLibrary.BrowseDirectoryAsync(request);
+            return ResponseHelper.Ok(result);
+        }
+
         private static void ValidateFileId(int id)
         {
             if (id > 0)

Avalonia-Services/Services/FileLibrary/FileLibraryService.cs

@@ -261,6 +261,54 @@ namespace Avalonia_Services.Services.FileLibrary
                 .FirstOrDefaultAsync(cancellationToken);
         }
 
+        public async Task<BrowseDirectoryResponse> BrowseDirectoryAsync(BrowseDirectoryRequest request, CancellationToken cancellationToken = default)
+        {
+            var rootId = request.RootId;
+            // URL 友好的正斜杠，用于响应和内存处理
+            var prefix = (request.Path ?? "").Trim().Replace('\\', '/').Trim('/');
+            // Windows 反斜杠，用于数据库查询
+            var dbPrefix = prefix.Replace('/', '\\');
+
+            var query = db.ManagedFileRecords
+                .AsNoTracking()
+                .Where(f => f.LibraryRootId == rootId && f.Exists
+                    && f.LibraryRoot != null && f.LibraryRoot.IsAvailable);
+
+            if (!string.IsNullOrEmpty(dbPrefix))
+            {
+                var dbPrefixWithSlash = dbPrefix + "\\";
+                query = query.Where(f => f.RelativePath.StartsWith(dbPrefixWithSlash));
+            }
+
+            var allFiles = await query.ToListAsync(cancellationToken);
+
+            var subdirs = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            var currentFiles = new List<FileRecordDto>();
+
+            foreach (var file in allFiles)
+            {
+                var relativePath = file.RelativePath.Replace('\\', '/');
+                var remaining = string.IsNullOrEmpty(prefix)
+                    ? relativePath
+                    : relativePath[(prefix.Length + 1)..];
+
+                var slashIndex = remaining.IndexOf('/');
+                if (slashIndex < 0)
+                {
+                    currentFiles.Add(ToFileDto(file));
+                }
+                else
+                {
+                    subdirs.Add(remaining[..slashIndex]);
+                }
+            }
+
+            return new BrowseDirectoryResponse(
+                prefix,
+                subdirs.OrderBy(d => d, StringComparer.OrdinalIgnoreCase).ToList(),
+                currentFiles);
+        }
+
         public async Task<TextPreviewDto?> GetTextPreviewAsync(int id, CancellationToken cancellationToken = default)
         {
             var file = await db.ManagedFileRecords

Avalonia-Services/Services/FileLibrary/IFileLibraryEndpointService.cs

@@ -24,5 +24,7 @@ namespace Avalonia_Services.Services.FileLibrary
         Task<IApiResponse> GetFileAsync(FileQueryRequest request);
 
         Task<IApiResponse> GetTextPreviewAsync(FileQueryRequest request);
+
+        Task<IApiResponse> BrowseDirectoryAsync(BrowseDirectoryRequest request);
     }
 }

Avalonia-Services/Services/FileLibrary/IFileLibraryService.cs

@@ -25,5 +25,7 @@ namespace Avalonia_Services.Services.FileLibrary
         Task<FileRecordDto?> GetFileAsync(int id, CancellationToken cancellationToken = default);
 
         Task<TextPreviewDto?> GetTextPreviewAsync(int id, CancellationToken cancellationToken = default);
+
+        Task<BrowseDirectoryResponse> BrowseDirectoryAsync(BrowseDirectoryRequest request, CancellationToken cancellationToken = default);
     }
 }