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]>

LICENSE.md

@@ -0,0 +1,45 @@
+# Licensing
+
+This project is under **two** licences, because it has to be.
+
+| Path | Licence |
+|---|---|
+| `hardware/`, `docs/`, `README.md` | **CC BY-NC-SA 4.0** — [`LICENSES/CC-BY-NC-SA-4.0.txt`](LICENSES/CC-BY-NC-SA-4.0.txt) |
+| `firmware/` | **GPL-2.0-or-later** — [`LICENSES/GPL-2.0.txt`](LICENSES/GPL-2.0.txt) |
+| `Documents/` | Third-party vendor datasheets. Not mine to license. |
+
+## The hardware: CC BY-NC-SA 4.0
+
+Build one, change it, share what you change — but don't sell it.
+
+- **BY** — credit the original.
+- **NC** — no commercial use.
+- **SA** — derivatives must carry this same licence.
+
+### Two things to be clear about
+
+**This is not "open source" or "open hardware" by the formal definitions.** Both
+the OSI and OSHWA definitions require permitting commercial use, so a
+NonCommercial term disqualifies it. That is a deliberate choice here, not an
+oversight — but it means OSHWA will not certify it, some people will decline to
+contribute on principle, and it cannot be called open source without being
+wrong.
+
+**"NonCommercial" is genuinely fuzzy.** Creative Commons defines it as use "not
+primarily intended for or directed toward commercial advantage or monetary
+compensation." That leaves real ambiguity: a fab house charging to make you a
+board is fine, a company using it internally is arguable, someone selling
+assembled units is not. Enforcement is on the copyright holder.
+
+## The firmware: GPL-2.0, and it cannot be otherwise
+
+Anything derived from QMK is GPL-2.0, and **the GPL explicitly permits
+commercial use**. A NonCommercial restriction cannot be added to GPL-derived
+code — doing so would violate the GPL and make the result undistributable.
+
+So the firmware in this repo is GPL-2.0-or-later. Someone may legally sell
+firmware derived from it. That is not a gap in the licensing; it is the price of
+building on QMK, and there is no version of this project where it isn't true.
+
+The hardware restriction still stands on its own: the thing you would need to
+*build and sell* is the board, and that is NC.