Based Linux GRUB gfxmenu theme, generated by based-brand.

Install this directory as /boot/grub/themes/based-linux/ and point GRUB at it
through an /etc/default/grub.d drop-in:

    GRUB_THEME=/boot/grub/themes/based-linux/theme.txt

(the grub overlay's theme: based-linux config key emits exactly that; GRUB_THEME
wins over GRUB_BACKGROUND when both are set).

Asset the build pipeline must supply into this directory:

    background.png    menu background, cover-fit to the GRUB resolution
                      (e.g. 1920x1080); referenced by desktop-image

Optional assets (the theme renders without them):

    terminal_box_*.png    styled-box slices (terminal_box_c.png, _n,
                          _ne, _nw, _s, _se, _sw, _e, _w) for the GRUB
                          command-line terminal window

No fonts are referenced: every text element uses GRUB's built-in font,
so the theme never depends on .pf2 files being installed.
