feat(branding): ISO boot splash from the vendored Nomarchy logo

Vendor the vector logo from the legacy branch
(modules/nixos/branding/logo.svg) and use it for the live ISO's isolinux
splash: rsvg-convert renders it, recolored to the palette accent and
centred on the theme base (from theme-state.json) at build time, wired via
isoImage.splashImage in hosts/live.nix. Verified the generated PNG by
building it in the sandbox.

UEFI/GRUB still uses the stock theme (grubTheme needs a full theme dir —
left on the roadmap), as does the distroId switch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

hosts/live.nix

@@ -3,11 +3,27 @@
 # exists to test the distro end-to-end on real hardware.
 { lib, pkgs, username, nomarchySrc, ... }:
 
+let
+  # ISO boot splash: the Nomarchy monogram recolored to the palette accent,
+  # centred on the theme base. Built from the vendored vector logo and the
+  # live theme-state.json (tokyo-night by default). Shows on the isolinux
+  # (BIOS) boot menu; UEFI/GRUB still uses the stock theme (see roadmap).
+  state = builtins.fromJSON (builtins.readFile ../theme-state.json);
+  isoColor = key: fallback: lib.removePrefix "#" ((state.colors or { }).${key} or fallback);
+  isoSplash = pkgs.runCommand "nomarchy-iso-splash.png"
+    { nativeBuildInputs = [ pkgs.imagemagick pkgs.librsvg ]; } ''
+    rsvg-convert -h 320 ${../modules/nixos/branding/logo.svg} > logo.png
+    magick logo.png -fill "#${isoColor "accent" "7aa2f7"}" -colorize 100 logo-c.png
+    magick -size 1920x1080 xc:"#${isoColor "base" "1a1b26"}" \
+      logo-c.png -gravity center -composite $out
+  '';
+in
 {
   networking.hostName = "nomarchy-live";
 
   isoImage.volumeID = lib.mkForce "NOMARCHY_LIVE";
   isoImage.edition = lib.mkForce "live";
+  isoImage.splashImage = isoSplash;
 
   # The minimal-CD profile slims the image for a CONSOLE installer; this
   # ISO is the desktop, so re-enable what it strips. Above all