refactor(steps-guix): align linux64 handover with upstream jump flow and end with shared after

steps-guix/improve/after.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+exec /steps/improve/after.sh

steps-guix/jump/linux64.sh

@@ -1,7 +1,4 @@
 #!/bin/bash
-#
-# SPDX-FileCopyrightText: 2026 Luo Yanpan
-#
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 set -e

steps-guix/linux-6.12.74/pass1.sh

@@ -1,5 +1,3 @@
-# SPDX-FileCopyrightText: 2026 Luo Yanpan
-#
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 : "${KERNEL_SYSROOT:=/kernel-toolchain}"

steps-guix/manifest

@@ -10,7 +10,7 @@ build: musl-fts-1.2.7
 build: musl-obstack-1.2.3
 build: elfutils-0.194
 build: linux-6.12.74
-improve: linux64
+jump: linux64
 build: libgpg-error-1.59
 build: libgcrypt-1.12.1
 build: guile-gcrypt-0.5.0