[feature] Custom app icon and logo

[Ampedeath]

Currently using the default create-tauri-app icon set (src-tauri/icons/) — looks like a generic dev-tool icon, not an app logo (visible next to real app icons in the system tray).

• Design a simple, recognizable WorkMemory icon/logo
• Regenerate the full icon set via npm run tauri icon <source.png> (covers .ico, .icns, all PNG sizes)
• Replace src-tauri/icons/ and rebuild