licence: SchOS is GPL-2.0-or-later, no longer Apache-2.0

Nexoniarz is the sole author and SchOS was never published under
Apache-2.0, so this is a straight relicence. LICENSE is the FSF GPLv2 text,
every first-party SPDX header moves to GPL-2.0-or-later, and NOTICE,
README.md, docs/licensing.md and the site say so. projects/schfs-linux
follows the rest of the tree.

The GPL gives copyleft: a fork has to ship its source. It also lifts the
old "Linux drivers, never" rule, since GPL-2.0-only code combines with
GPL-2.0-or-later. "Or later" leaves room for GPLv3, but one binary still
has to pick one version, so docs/licensing.md now keeps Apache-2.0 and
GPLv3 code out of the kernel to keep Linux code possible there. BSD
4-clause code goes from "avoid" to "no", because the advertising clause
is GPL-incompatible.

LDLS still ships no .ko. That boundary is now project policy rather than
a legal requirement, and ldls.md, devices.md and licensing.md section 6
say so. refmod declares license=GPL, and ldls-check passes (27 checks).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Makefile

@@ -455,8 +455,8 @@ RAMDISK_BLOCKS ?= 8000
 # rule before it is a size one: the ramdisk image is linked *into the kernel
 # binary*, so anything staged in sysroot/ when it is built becomes part of a
 # distributable artifact. Anything that arrives in sysroot/ under a licence that
-# cannot be combined with Apache-2.0, or that simply is not ours to redistribute,
-# belongs on this list rather than in someone's memory.
+# cannot be combined with GPL-2.0-or-later, or that simply is not ours to
+# redistribute, belongs on this list rather than in someone's memory.
 #
 # This is not hypothetical: a 33 MB test payload once landed here and overflowed
 # the 6 MB image, and mkfs's "increase FSSIZE" message then pointed at a constant