v1.2.0 - Backup & Desktop Integration

🆕 Local Backup/Restore
• Export all notes as JSON
• 3 restore modes (Merge/Replace/Overwrite)
• Auto-backup before restore

🆕 Markdown Desktop Integration (optional)
• .md export for desktop editors (WebDAV mount)
• Last-Write-Wins sync
• Manual import

📚 Sync architecture docs