Smarter Mac notifications, better attachment handling, and clearer version info.

This release focuses on reliability and everyday usability on macOS:

• Actionable notifications: Reply, mark as read, or delete messages directly from macOS notifications to stay in flow.
• Improved attachment handling: You can now open and save files even if their filenames contain special or previously unsupported characters.
• Clearer About dialog: Desktop and WebApp version numbers are now displayed more clearly for easier reference.
• Updated macOS app icon: The icon has been refreshed to better match modern macOS layout standards.

Together, these improvements make the desktop app more robust, more transparent, and easier to use day to day.