v1.3.0

• Changed the tab-bar + and Cmd/Ctrl+N into a dedicated New Markdown flow that creates a .md file in the current document folder and opens it directly in source edit.
• Added 700 ms debounced autosave in source edit mode, so quick edits persist without switching back to preview or pressing Save.
• Forced pending edits to save before preview, tab activation, tab close, window close, and app quit, including protection against stale autosave acknowledgements.
• Kept tabs open and editor contents intact when saving fails, with a visible error that explains the affected path.
• Protected dirty editor contents from external file-change reloads and stopped time-only watcher suppression from hiding real external writes.
• Verified the native macOS update menu, Sparkle configuration, signed appcast contract, and live GitHub desktop release selection.