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.c

@@ -0,0 +1,37 @@
+#include "midi_uart.h"
+#include "hardware/gpio.h"
+#include "hardware/uart.h"
+
+#define PIN_OUT_KIT     0   /* UART0 TX */
+#define PIN_IN        1   /* UART0 RX, 6N137 output with a 1 kΩ pull-up on the board */
+#define PIN_OUT_SYNTH 4   /* UART1 TX */
+#define MIDI_BAUD     31250
+
+static uart_inst_t *const PORTS[2] = { uart0, uart1 };
+
+void midi_init(void){
+  uart_init(uart0, MIDI_BAUD);
+  uart_init(uart1, MIDI_BAUD);
+  uart_set_format(uart0, 8, 1, UART_PARITY_NONE);
+  uart_set_format(uart1, 8, 1, UART_PARITY_NONE);
+  gpio_set_function(PIN_OUT_KIT, GPIO_FUNC_UART);
+  gpio_set_function(PIN_IN, GPIO_FUNC_UART);
+  gpio_set_function(PIN_OUT_SYNTH, GPIO_FUNC_UART);   /* GP5 (UART1 RX) stays a matrix row */
+  gpio_pull_up(PIN_IN);
+  /* each MIDI current loop draws 6–8 mA, above the 4 mA default */
+  gpio_set_drive_strength(PIN_OUT_KIT, GPIO_DRIVE_STRENGTH_12MA);
+  gpio_set_drive_strength(PIN_OUT_SYNTH, GPIO_DRIVE_STRENGTH_12MA);
+}
+
+void midi_send(int port, const uint8_t *bytes, int n){ uart_write_blocking(PORTS[port], bytes, (size_t)n); }
+
+void midi_note_on(int port, int ch, int note, int vel){
+  uint8_t m[3] = { (uint8_t)(0x90 | (ch & 15)), (uint8_t)(note & 127), (uint8_t)(vel & 127) };
+  midi_send(port, m, 3);
+}
+void midi_note_off(int port, int ch, int note){
+  uint8_t m[3] = { (uint8_t)(0x80 | (ch & 15)), (uint8_t)(note & 127), 0 };
+  midi_send(port, m, 3);
+}
+
+int midi_in_read(void){ return uart_is_readable(uart0) ? uart_getc(uart0) : -1; }