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>

tools/python/ldls_check.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# SPDX-License-Identifier: Apache-2.0
+# SPDX-License-Identifier: GPL-2.0-or-later
 #
 # Check the LDLS loader against an object we compiled ourselves.
 #
@@ -47,7 +47,7 @@ def main():
     # straight out of .modinfo. That is the first question anyone should be
     # able to ask about an object before loading it.
     need("module    refmod" in out, "the module names itself from .modinfo")
-    need("license   Apache-2.0" in out,
+    need("license   GPL" in out,
          "the declared licence is read without loading anything")
 
     # Every kind of section the loader has to place.