feat: add markdown editor component with extensible toolbar system

- Add SbMarkdownEditor component with EasyMDE and CodeMirror integration
  - Implement IMdToolbarContributor interface for extensible toolbar customization
  - Add MdToolbarService and MdToolbarOptions for toolbar management
  - Include vendor libraries (CodeMirror, EasyMDE, Mermaid, Highlight.js)
  - Add markdown editor interop and JavaScript integration
  - Refactor SbMarkdownViewer to support both embedded and standalone modes
  - Add demo page and localization keys for markdown editor
  - Normalize whitespace and line endings across all component files

tests/Forms/SbTextFieldTests.cs

@@ -1,4 +1,5 @@
 using Bunit;
+using Microsoft.AspNetCore.Components;
 using SufiChain.SufiBlazor.Components.Forms;
 using Xunit;