Add licensing: CC BY-NC-SA 4.0 hardware, GPL-2.0 firmware

Hardware and docs get CC BY-NC-SA 4.0 - build it, change it, share changes,
no commercial products. Firmware has to be GPL-2.0 because it derives from
QMK, and the GPL forbids adding a NonCommercial restriction, so that half
permits commercial use whether we like it or not.

LICENSE.md records both, plus the two honest caveats: NC means this is not
open source by the OSI or OSHWA definitions, and NonCommercial is a vague
term whose enforcement falls on the copyright holder.

Co-Authored-By: Claude Opus 5 <[email protected]>

README.md

@@ -22,13 +22,16 @@ maps across the three boards.
 
 ## Licence
 
-Not yet chosen. Until one is added, default copyright applies: you may read
-this, but not build, fork or reuse it. If that isn't the intent, add
-CERN-OHL-S or TAPR OHL for the hardware, and GPL-2.0 for anything derived from
-QMK.
+**Hardware and documentation: [CC BY-NC-SA 4.0](LICENSES/CC-BY-NC-SA-4.0.txt).**
+Build one, modify it, share your modifications under the same terms — but no
+commercial products.
 
-The PDFs under `Documents/` are vendor datasheets (WCH, ST) redistributed for
-convenience and are **not** covered by whatever licence this repo adopts.
+**Firmware: [GPL-2.0-or-later](LICENSES/GPL-2.0.txt)**, forced by QMK, which
+permits commercial use. See [`LICENSE.md`](LICENSE.md) for why the two can't be
+the same, and for the caveats on what "NonCommercial" actually means.
+
+Datasheets under `Documents/` are third-party vendor PDFs and aren't covered by
+either.
 
 ---
 
@@ -337,6 +340,6 @@ Per house convention. This one is unusually clean:
       scrubbing needed, unlike most repos here.
 - [ ] Confirm no JLC/LCSC account identifiers end up in fab exports.
 - [x] Scanned: no LAN topology, credentials or personal data in files or history.
-- [ ] **Licence still unchosen** — see the Licence section above.
+- [x] Licence chosen: CC BY-NC-SA 4.0 (hardware) + GPL-2.0 (firmware).
 - [ ] Vendor datasheets in `Documents/` are redistributed third-party PDFs.
       Consider linking instead of vendoring if that matters to you.