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/app/storage.c

@@ -0,0 +1,73 @@
+#include "storage.h"
+#include "hardware/flash.h"
+#include "pico/flash.h"
+#include <stddef.h>
+#include <string.h>
+
+#define MAGIC   0x53425831u   /* "SBX1" */
+#define VERSION 2             /* 2: ROOT / SCALE added, BANK gone. Older records are ignored. */
+#define OFFSET  (PICO_FLASH_SIZE_BYTES - FLASH_SECTOR_SIZE)
+#define BUFSZ   512
+
+typedef struct {
+  uint32_t magic, version;
+  uint32_t seed, salts[2];
+  int32_t gen, bpm, scale, root, mono_ch, mono_oct;
+  uint8_t on[SB_NT];
+  pad_t learn[NKIT];
+  slot_t slots[NSLOTS];
+  uint32_t crc;
+} record_t;
+_Static_assert(sizeof(record_t) <= BUFSZ, "record too big");
+
+static uint32_t crc(const record_t *r){
+  const uint8_t *p = (const uint8_t *)r;
+  uint32_t h = 0x811C9DC5u;
+  size_t i;
+  for(i = 0; i < offsetof(record_t, crc); i++) h = (h ^ p[i]) * 0x01000193u;
+  return h;
+}
+
+/* defaults from app.js DEF and app */
+void storage_defaults(live_t *L, slot_t *slots){
+  int t;
+  memset(L, 0, sizeof *L);
+  L->state.seed = 0x5EEDB0C5u;
+  L->gen = 0; L->scale = -1; L->root = -1; L->energy = 64; L->drift = 32; L->bpm = 165;
+  for(t = 0; t < SB_NT; t++) L->on[t] = 1;
+  L->mono_ch = 1; L->mono_oct = 0; L->clock = 1;
+  memset(slots, 0, sizeof(slot_t) * NSLOTS);
+}
+
+int storage_load(live_t *L, slot_t *slots){
+  const record_t *r = (const record_t *)(XIP_BASE + OFFSET);
+  int t;
+  storage_defaults(L, slots);
+  if(r->magic != MAGIC || r->version != VERSION || r->crc != crc(r)) return 0;
+  L->state.seed = r->seed; L->state.salts[0] = r->salts[0]; L->state.salts[1] = r->salts[1];
+  L->gen = r->gen; L->bpm = r->bpm; L->scale = r->scale; L->root = r->root; L->mono_ch = r->mono_ch; L->mono_oct = r->mono_oct;
+  for(t = 0; t < SB_NT; t++) L->on[t] = r->on[t] ? 1 : 0;
+  memcpy(L->learn, r->learn, sizeof L->learn);
+  memcpy(slots, r->slots, sizeof r->slots);
+  return 1;
+}
+
+static void do_write(void *buf){
+  flash_range_erase(OFFSET, FLASH_SECTOR_SIZE);
+  flash_range_program(OFFSET, (const uint8_t *)buf, BUFSZ);
+}
+
+int storage_save(const live_t *L, const slot_t *slots){
+  static uint8_t buf[BUFSZ] __attribute__((aligned(4)));
+  record_t *r = (record_t *)buf;
+  memset(buf, 0xFF, sizeof buf);
+  memset(r, 0, sizeof *r);
+  r->magic = MAGIC; r->version = VERSION;
+  r->seed = L->state.seed; r->salts[0] = L->state.salts[0]; r->salts[1] = L->state.salts[1];
+  r->gen = L->gen; r->bpm = L->bpm; r->scale = L->scale; r->root = L->root; r->mono_ch = L->mono_ch; r->mono_oct = L->mono_oct;
+  memcpy(r->on, L->on, sizeof r->on);
+  memcpy(r->learn, L->learn, sizeof r->learn);
+  memcpy(r->slots, slots, sizeof r->slots);
+  r->crc = crc(r);
+  return flash_safe_execute(do_write, buf, 500) == PICO_OK;
+}