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/app.h

@@ -0,0 +1,45 @@
+/* Seedbox firmware: state shared between core 0 (UI) and core 1 (sequencer). Mirrors sim/app.js. */
+#ifndef SEEDBOX_APP_H
+#define SEEDBOX_APP_H
+
+#include <stdint.h>
+#include "pico/critical_section.h"
+#include "pico/util/queue.h"
+#include "engine.h"
+
+#define NKIT   7     /* kit tracks are 0..6 (lane 0); LEARN index = track index */
+#define NSLOTS 8
+
+typedef struct { uint8_t used, ch, note; } pad_t;   /* learned pad: ch 0..15 */
+
+/* Everything the sequencer reads. Core 0 writes it under g_live_lock; core 1 copies it under the same lock. */
+typedef struct {
+  sb_state state;
+  int gen, energy, drift, bpm;
+  int scale, root;                 /* ROOT / SCALE pages: -1 = AUTO (the seed picks) */
+  uint8_t on[SB_NT], inv[SB_NT];   /* inv: flipped while the button is held */
+  pad_t learn[NKIT];
+  int mono_ch;                     /* synth channel 1..16 */
+  int mono_oct;                    /* -3..3 */
+  int clock;                       /* send clock + start/stop */
+} live_t;
+
+extern live_t g_live;
+extern critical_section_t g_live_lock;
+
+/* core 0 -> core 1 */
+enum { CMD_START, CMD_STOP, CMD_RELEASE_TRACK, CMD_BPM };
+typedef struct { uint8_t cmd; int16_t arg; } cmd_t;
+extern queue_t g_cmdq;
+
+/* core 1 -> core 0, for the screen */
+extern volatile int g_running;
+extern volatile int g_cur_bar;                 /* bar being heard, -1 if none */
+extern volatile uint32_t g_hit_until_ms[SB_NT];
+
+void seq_core1_main(void);
+
+/* app.js learned(): the channel and note a kit track was learned with. Returns 0 if not learned. */
+int learned(const live_t *L, int tr, int *ch, int *note);
+
+#endif