fix: handle "index" files in root directory correctly in URL path generation

- Updated `FileSystemUtilities.FilePathToUrlPath` to return an empty URL path for `index` files in the root directory.
- Adjusted related test case to validate the new behavior.

Author: phil-scott-78

src/MyLittleContentEngine/Services/Infrastructure/FileSystemUtilities.cs

@@ -23,6 +23,12 @@ public UrlPath FilePathToUrlPath(FilePath filePath, FilePath baseContentPath)
         var directoryPath = _filePathOps.GetDirectory(relativePath);
         var fileNameWithoutExtension = _filePathOps.GetFileNameWithoutExtension(relativePath).Slugify();
 
+        // index.md represents the directory itself, not a page called "index"
+        if (fileNameWithoutExtension.Equals("index", StringComparison.OrdinalIgnoreCase))
+        {
+            return directoryPath.IsEmpty ? UrlPath.Empty : directoryPath.ToUrlPath();
+        }
+
         var result = _filePathOps.Combine(directoryPath, fileNameWithoutExtension);
         return result.ToUrlPath();
     }

tests/MyLittleContentEngine.Tests/Infrastructure/FileSystemUtilitiesTests.cs

@@ -147,7 +147,7 @@ public void ValidateDirectoryPath_NonExistingDirectory_ThrowsDirectoryNotFoundEx
     }
 
     [Fact]
-    public void FilePathToUrlPath_FileInRootDirectory_ReturnsJustFilename()
+    public void FilePathToUrlPath_IndexFileInRootDirectory_ReturnsEmpty()
     {
         var fileSystem = new MockFileSystem();
         var pathUtilities = CreateFileSystemUtilities(fileSystem);
@@ -156,7 +156,7 @@ public void FilePathToUrlPath_FileInRootDirectory_ReturnsJustFilename()
 
         var result = pathUtilities.FilePathToUrlPath(filePath, baseContentPath);
 
-        result.Value.ShouldBe("index");
+        result.IsEmpty.ShouldBeTrue();
     }
 
     [Fact]