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/midi_uart.h

@@ -0,0 +1,15 @@
+/* MIDI over the two UARTs: OUT KIT = UART0 TX (GP0), OUT SYNTH = UART1 TX (GP4), IN = UART0 RX (GP1). 31 250 baud, 8N1. */
+#ifndef SEEDBOX_MIDI_UART_H
+#define SEEDBOX_MIDI_UART_H
+
+#include <stdint.h>
+
+enum { MIDI_KIT = 0, MIDI_SYNTH = 1 };
+
+void midi_init(void);
+void midi_send(int port, const uint8_t *bytes, int n);   /* blocking */
+void midi_note_on(int port, int ch, int note, int vel);  /* ch 0..15 */
+void midi_note_off(int port, int ch, int note);
+int  midi_in_read(void);                                 /* next byte from MIDI IN, or -1 */
+
+#endif