Replace AI-generated app icon with professionally designed icon

[fbal98]

Problem

The current app icon appears to be AI-generated and lacks the polish and intentionality expected for a professional macOS app.

Goal

Create or commission a professional, hand-crafted icon that:

• Reflects CopyPrompt's core purpose (instant prompt access)
• Works well at all sizes (16px to 1024px)
• Maintains clarity in the menu bar (16-24px) and app switcher
• Respects macOS design conventions and Sonoma aesthetic
• Looks sharp in both light and dark modes

Design Considerations

• Menu bar icon: Should be recognizable at 16-24px
• App icon: Should work across all AppKit sizes (16, 32, 64, 128, 256, 512, 1024)
• Style: Modern, minimal, native to macOS
• Assets location: CopyPrompt/Assets.xcassets/AppIcon.appiconset/

Next Steps

1. Sketch design concepts
2. Get feedback
3. Finalize and export at all required sizes
4. Update AppIcon.appiconset