Debian Linux Full Rebrand

I want a fully customised Debian-based distribution that carries my visual identity from the very first boot screen through to the desktop environment. This means replacing the splash/boot animation, GRUB theme, wallpapers, icon set, GTK/Qt theme and default fonts with artwork I will supply (or that you can create to match my style guide).

Beyond appearance, the distro should still behave like standard Debian so that users can access the usual repositories and updates without breaking anything. No extra software needs to be bundled unless it is required for the theming itself.

Deliverables
• Bootable ISO (UEFI & Legacy) with all branding elements applied
• Source files or scripts used for the build so I can reproduce future versions
• Short read-me outlining how to update artwork or rebuild the image

I will test the ISO in both VirtualBox and on bare metal; it should install cleanly and display my branding at every stage.