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>

firmware/drivers/inputs.h

@@ -0,0 +1,17 @@
+/* Button matrix (rows GP2 GP3 GP5, columns GP6–GP9), SEED (GP13), RUN (GP14), encoder push (GP12).
+   All active-low with pull-ups (RP2350 erratum E9). Call inputs_scan() about once per millisecond. */
+#ifndef SEEDBOX_INPUTS_H
+#define SEEDBOX_INPUTS_H
+
+#include <stdint.h>
+
+/* bit index: matrix key = row * 4 + col (row 0..2, col 0..3), then the switches */
+enum { IN_MATRIX = 12, IN_SEED = 12, IN_RUN = 13, IN_PUSH = 14, IN_COUNT = 15 };
+
+/* matrix key -> track index (engine order), -1 = no button. Same as PANEL in app.js. */
+extern const int8_t INPUT_KEY_TRACK[12];
+
+void     inputs_init(void);
+uint32_t inputs_scan(void);   /* returns the debounced state, bit set = pressed / RUN on */
+
+#endif