Add native Crystal exploration port and reference tooling

tests/synthetic-rom.ts

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+/** Original test cartridge: no Nintendo logo, boot ROM, graphics, or game code.
+ * A tiny CPU loop draws a striped tile and writes joypad reads to battery RAM.
+ * This intentionally bypasses the product ROM gate ONLY in the test harness.
+ */
+export function syntheticRom(): Uint8Array {
+  const rom = new Uint8Array(32768);
+  rom.set([0xc3, 0x50, 0x01], 0x100); // JP $0150
+  rom.set(new TextEncoder().encode("CRYSTALTEST"), 0x134);
+  rom[0x143] = 0x80; // CGB-capable
+  rom[0x147] = 0x10; // MBC3 + RTC + RAM + battery
+  rom[0x148] = 0;
+  rom[0x149] = 3; // 32 KiB RAM
+  const code = [
+    0xf3, // DI
+    0x31,
+    0xfe,
+    0xff, // LD SP,$fffe
+    0xaf,
+    0xe0,
+    0x40, // LCD off
+    0x3e,
+    0x0a,
+    0xea,
+    0,
+    0, // enable cartridge RAM
+    0x3e,
+    0x80,
+    0xe0,
+    0x68, // CGB background palette auto-increment
+    0x3e,
+    0xff,
+    0xe0,
+    0x69,
+    0x3e,
+    0x7f,
+    0xe0,
+    0x69, // white
+    0xaf,
+    0xe0,
+    0x69,
+    0xe0,
+    0x69, // black
+    0x21,
+    0,
+    0x80,
+    0x06,
+    0x10,
+    0x3e,
+    0xaa, // HL=$8000, B=16, A=$aa
+    0x22,
+    0x05,
+    0x20,
+    0xfc, // tile pattern
+    0x3e,
+    0xe4,
+    0xe0,
+    0x47, // DMG palette
+    0x3e,
+    0x91,
+    0xe0,
+    0x40, // LCD on, background tile 0
+  ];
+  const loop = 0x150 + code.length;
+  code.push(
+    0x3e,
+    0x10,
+    0xe0,
+    0,
+    0xf0,
+    0,
+    0xea,
+    0,
+    0xa0,
+    0xc3,
+    loop & 255,
+    loop >> 8,
+  );
+  rom.set(code, 0x150);
+  let checksum = 0;
+  for (let i = 0x134; i <= 0x14c; i++) checksum = (checksum - rom[i] - 1) & 255;
+  rom[0x14d] = checksum;
+  return rom;
+}