Use create-dmg for proper DMG icon embedding

- Replace manual hdiutil + fileicon with create-dmg
- create-dmg embeds icons in DMG internal structure
- Icons will persist through HTTP downloads

Use create-dmg for proper DMG icon embedding

- Replace manual hdiutil + fileicon with create-dmg
- create-dmg embeds icons in DMG internal structure
- Icons will persist through HTTP downloads

Add DMG file icon using fileicon

Add volume icon to DMG in CI build

Fix: add write permissions for GitHub release