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/branding/README.md

@@ -55,7 +55,7 @@ the kernel's name (**SchIFT**) as a shape.
   coverage mask carries none, so the loader draws it in metal and the kernel in
   the theme accent, from the same bytes.
 - **With or without a wordmark.** Set "SchOS" beside it in **Roboto Bold**,
-  which is already in the tree (`ports/Roboto`), already Apache-2.0, and already
+  which is already in the tree (`ports/Roboto`), Apache-2.0, and already
   in `NOTICE`.
 - Non-human and non-animal, permanently. If a character is ever drawn it gets
   its own mark; a logo that starts growing a face has taken that job.