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>

docs/architecture/ldls.md

@@ -54,9 +54,10 @@ ships the layer and never the thing it loads. `.gitignore` refuses `*.ko`,
 is deliberately not part of `all`, and `make ldls-unstage` takes it out again.
 
 [../licensing.md](../licensing.md) §6 is the whole argument. The short form is
-that GPL obligations attach to *distribution*, we distribute Apache-2.0 code
-containing no GPL, and the combination happens in a user process on the user's
-machine — so no combined work is distributed by anyone.
+that the combination happens in a user process on the user's machine, so no
+combined work is distributed by anyone. Since SchOS moved to GPL-2.0-or-later
+that is no longer the only way it *could* be done — it is the way it is done,
+because a module we never ship is a module we never have to answer for.
 
 ### 2. It runs in a process, never in the kernel