Make diagrams self-contained and lead the README with them

The SVGs relied on stylesheet classes supplied by the tool that rendered them
- outside it they were black boxes with invisible text. Each now carries its
own <style> block with light and dark palettes.

Also regenerates the overview, which still showed the old row-staggered 36/39
halves, and adds a licence section: nothing is chosen yet, so default
copyright applies.

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

README.md

@@ -1,10 +1,35 @@
 # tertiary
 
-A three-piece keyboard: two mirrored halves plus a numpad/nav/media board that
-also carries the USB hub. One cable reaches the computer.
+A three-piece keyboard: two column-staggered halves plus a numpad/nav/media
+board that also carries the USB hub. One cable reaches the computer.
 
 Status: **design**. No boards ordered, no firmware written.
 
+![All three boards to scale](docs/three-board-overview.svg)
+
+<table>
+<tr>
+<td><img src="docs/half-left-staggered.svg" alt="Left half, 34 keys"></td>
+<td><img src="docs/half-right-staggered.svg" alt="Right half, 41 keys"></td>
+</tr>
+</table>
+
+![Numpad layout](docs/numpad-layout.svg)
+
+Derived from a full 104 rather than a compact ergo core — see
+[`docs/104-key-split.svg`](docs/104-key-split.svg) for how the original layout
+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.
+
+The PDFs under `Documents/` are vendor datasheets (WCH, ST) redistributed for
+convenience and are **not** covered by whatever licence this repo adopts.
+
 ---
 
 ## The three boards
@@ -311,5 +336,7 @@ Per house convention. This one is unusually clean:
 - [ ] Nothing here touches LAN topology, credentials, or personal data — no
       scrubbing needed, unlike most repos here.
 - [ ] Confirm no JLC/LCSC account identifiers end up in fab exports.
-- [ ] Decide on a licence before publishing hardware files (CERN-OHL-S or
-      TAPR OHL for hardware; GPL2 for anything derived from QMK).
+- [x] Scanned: no LAN topology, credentials or personal data in files or history.
+- [ ] **Licence still unchosen** — see the Licence section above.
+- [ ] Vendor datasheets in `Documents/` are redistributed third-party PDFs.
+      Consider linking instead of vendoring if that matters to you.