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>

ports/Makefile

@@ -1,6 +1,6 @@
-# SPDX-License-Identifier: Apache-2.0
+# SPDX-License-Identifier: GPL-2.0-or-later
 # SchOS ports — third-party software, one directory per port.
-# All ports are permissive-licensed (MIT, BSD, 0BSD, Apache 2.0).
+# Every port's licence must combine with GPL-2.0-or-later; see docs/licensing.md.
 #
 #   ports/musl/    libc — installs headers/libs to build/ports/musl/prefix
 #   ports/mksh/    MirBSD Korn Shell — installed as sysroot/bin/sh
@@ -17,7 +17,7 @@
 
 # Ports that live in this directory but are deliberately not built by `make`.
 # Empty for now; the filter stays because the reason it existed will recur --
-# a port whose licence cannot be combined with Apache-2.0 can be kept here for
+# a port whose licence cannot be combined with GPL-2.0-or-later can be kept here for
 # local testing but must never be built into a SchOS image.
 NOTPORTS :=
 PORTS := $(filter-out $(NOTPORTS), \