Add GRUB EFI build recipe and chainload configuration

Builds GRUB 2.12 for the host machine (not Redox target) using template=custom.
Produces a 540 KiB standalone PE32+ EFI binary with GPT, FAT, ext2,
chainloader, and utility modules. The grub.cfg chainloads the Redox
bootloader from EFI/REDBEAR/redbear.efi.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

recipes/core/grub

@@ -0,0 +1 @@
+../../local/recipes/core/grub

recipes/wip/services/grub/recipe.toml

@@ -1,5 +0,0 @@
-#TODO compilation error
-[source]
-tar = "https://ftp.gnu.org/gnu/grub/grub-2.12.tar.xz"
-[build]
-template = "configure"

recipes/wip/services/grub/recipe.toml

@@ -0,0 +1 @@
+../../../../local/recipes/core/grub/recipe.toml