Seedbox v0.1 + firmware, generic kit/synth, ROOT/SCALE pages

First commit of the repo. Contents beyond the v0.1 simulator and layout:

- Full Pico 2 W firmware (firmware/app, drivers, engine port, host test).
- BANK page and 404 mode A/B removed; learned pads play exactly what was learned.
- 404/MiniFreak renamed to KIT/SYNTH throughout (jacks, code, sim, docs,
  layout labels; wiring rebuilt).
- ROLL returns to page select after a re-roll; a freshly learned track turns on.
- LCD contrast 66.
- ROOT and SCALE pages: 21 scales, AUTO = the seed picks; global and sticky.

Intended music change: the scale table grew from 8 to 21 and AUTO picks from
all of them, so every seed's scale changed. Vectors regenerated with
npm run vectors, plus new key-override cases. Flash record is now version 2.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,49 @@
+# CLAUDE.md
+
+Seedbox: a generative MIDI rhythm and melody machine for the Raspberry Pi Pico 2 W. v0.1 is a browser simulator with a finished engine, and a checked stripboard layout. The next job is the C firmware.
+
+Read first: `README.md`, `docs/concept.md`, `firmware/README.md`, `docs/decisions.md`.
+
+## Ground rules
+
+- **`sim/engine.js` is the musical reference.** The C engine must reproduce `test/vectors/` exactly. Don't "fix" the C to sound better: change the JS, listen, regenerate, commit both.
+- **Never regenerate the vectors to make a failing port pass.** `npm run vectors` is only for intended changes to the music. Say so in the commit message.
+- **Keep the engine integer-only and deterministic.**
+  - No `Math.random`, no floats in decisions, no wall-clock time.
+  - Use floor division through `fdiv`/`mod`.
+- **`hardware/layout.js` is the only source for the stripboard.**
+  - After any change, run `node hardware/check-layout.js`; it must print `layout clean`.
+  - Then run `node tools/build-wiring.js`.
+  - Don't hand-edit `tools/wiring.html`.
+- **Hardware facts that can't be checked here** (lug order on the user's TRS jacks, Nokia BL polarity): flag them; don't guess.
+- **RP2350**:
+  - Inputs use pull-ups (erratum E9).
+  - Set GP0/GP4 drive strength to 8–12 mA.
+  - The pin map in `docs/hardware/pinout.md` is fixed by the board that's being built; don't move pins without updating `layout.js` and re-running the checker.
+
+## Commands
+
+```sh
+npm test                          # vectors + layout, must pass before every commit
+npm run vectors                   # regenerate vectors (intended music changes only)
+node hardware/check-layout.js --nets
+node tools/build-wiring.js
+npx serve .  →  http://localhost:3000/sim/      # simulator (Web MIDI needs localhost/https)
+```
+
+No npm dependencies. Node 18+.
+
+## Layout
+
+- `sim/` simulator: `engine.js` (portable; also `require`-able from Node), `app.js` (browser UI, Web MIDI, scheduler, screen renderer), `index.html`.
+- `test/` `cases.js` (the case list), `render.js`, `gen-vectors.js`, `check-vectors.js`, `vectors/*.json`.
+- `hardware/` `layout.js`, `check-layout.js`.
+- `tools/` single-file bench pages: `wiring.html` (built), `bom.html`, `panel.html`; `wiring-src/` holds the parts `wiring.html` is built from.
+- `docs/` user-facing docs; `docs/hardware/svg` and the CSVs are exports from the tools.
+- `firmware/` empty except the plan. Suggested structure is in its README.
+
+## Conventions
+
+- The user (Gee) builds by hand: stripboard, hookup wire, panel-mount parts. Write instructions as strip letter + hole number, with colour roles from `docs/hardware/wiring.md`.
+- Docs are plain and short. Tables over prose for anything you'd look up.
+- Commit vectors and engine changes together. Commit layout and rebuilt wiring together.