feat: Update PostPageGenerator to enhance markdown processing and template file handling

Author: Arlodotexe

src/Blog/PostPage/PostPageGenerator.Markdown.cs

@@ -74,6 +74,7 @@ private string TransformMarkdownToHtml(string markdown)
             // Gap #1 resolution: Use Markdig Advanced Extensions pipeline
             var pipeline = new MarkdownPipelineBuilder()
                 .UseAdvancedExtensions()
+                .UseSoftlineBreakAsHardlineBreak()
                 .Build();
 
             return Markdown.ToHtml(markdown, pipeline);

src/Blog/PostPage/PostPageGenerator.Template.cs

@@ -82,15 +82,15 @@ private async Task CopyTemplateAssetsAsync(
                 var relativePath = await templateFolder.GetRelativePathToAsync(file);
 
                 // Create file at relative path in output folder (creates necessary parent folders)
-                var targetStorable = await outputFolder.CreateByRelativePathAsync(relativePath, StorableType.File, overwrite: true);
-                
+                var targetStorable = await outputFolder.CreateByRelativePathAsync(relativePath, StorableType.File);
                 if (targetStorable is not IFile targetFile)
                     throw new InvalidOperationException($"Created item at '{relativePath}' is not a file.");
 
                 // Copy file content
                 using var sourceStream = await file.OpenReadAsync();
-                using var targetStream = await targetFile.OpenStreamAsync(FileAccess.Write);
-                await sourceStream.CopyToAsync(targetStream);
+                using var destinationStream = await targetFile.OpenWriteAsync();
+                await sourceStream.CopyToAsync(destinationStream);
+                await destinationStream.FlushAsync();
             }
         }