MD Viewer v0.3.5

• Added line numbers to the Markdown editor in edit and split views, including synchronized scrolling and current-line highlighting.
• Added in-app document search with keyboard shortcuts, match counts, previous/next navigation, and close behavior.
• Added search highlighting in preview, edit, and split views without forcing view mode changes.
• Kept search highlights out of copy, HTML, DOCX, and print/PDF output.