Finish the opening milestone's switching, items and acceptance run

- Decode evolution lists from the ROM; all 251 match the pinned PRET source.
- Compare CalcMonStats and CalcExpAtLevel against the original routines in
  the reference emulator.
- Add a continuous opening playthrough from the intro to the catching
  tutorial, reloading a JSON save after every stage.
- Port player switching in battle: the PKMN menu, forced choices after a
  faint, Shift mode's offer and double faints, with the original texts.
- Port HP and status healing items in battle through the ROM's ItemEffects,
  HealingHPAmounts and StatusHealingActions tables.
- Add the battle party menu and the Items pocket to the UI.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/battle-driver.ts

@@ -0,0 +1,103 @@
+import type { CrystalAssets } from "../src/game/rom/assets";
+import type { TrainerData } from "../src/game/rom/trainers";
+import type {
+  Battle,
+  BattleEffect,
+  BattleInput,
+  BattleOptions,
+} from "../src/game/battle/battle";
+import type { Bag } from "../src/game/party/bag";
+import { generatePartyMon, type PartyMon } from "../src/game/party/pokemon";
+import { defaultTextContext } from "../src/game/scripts/text";
+
+export const partyMon = (
+  assets: CrystalAssets,
+  species: number,
+  level: number,
+): PartyMon =>
+  generatePartyMon(assets.pokemon, {
+    species,
+    level,
+    item: 0,
+    otId: 1234,
+    ot: "CHRIS",
+    dvs: 0x823b,
+    caughtData: 0,
+  });
+
+/** Battle options for a wild Pokémon or a ROM trainer, with a seeded
+ * stand-in for the hardware Random routine. */
+export function battleOptions(
+  assets: CrystalAssets,
+  trainers: TrainerData,
+  party: PartyMon[],
+  enemy:
+    | { wild: { species: number; level: number } }
+    | { trainer: [number, number] },
+  { seed = 1, bag }: { seed?: number; bag?: Bag } = {},
+): BattleOptions {
+  const base = {
+    data: assets.pokemon,
+    party,
+    bag,
+    playerId: 1234,
+    playerName: "CHRIS",
+    timeOfDay: 1,
+    pokedex: { seen: new Set<number>(), caught: new Set<number>() },
+    random: () => {
+      seed = (seed * 1103515245 + 12345) >>> 0;
+      return (seed >>> 16) & 255;
+    },
+    text: () => defaultTextContext("CHRIS"),
+  };
+  if ("wild" in enemy) return { ...base, wild: enemy.wild };
+  const trainer = trainers.trainer(...enemy.trainer);
+  return {
+    ...base,
+    trainer: {
+      name: trainer.name,
+      className: trainer.className,
+      party: trainers.createParty(trainer),
+      aiFlags: trainer.attributes.aiMoveFlags,
+      switchFlags: trainer.attributes.aiItemSwitchFlags,
+      reward: trainer.reward,
+    },
+  };
+}
+
+/** Run a battle. Menus take queued answers per prompt kind, then the
+ * defaults: the first move, YES, cancelling a move to forget and the
+ * first party slot. */
+export function playBattle(
+  battle: Battle,
+  queued: Partial<Record<BattleEffect["kind"], BattleInput[]>> = {},
+) {
+  const texts: string[] = [],
+    prompts: BattleEffect[] = [];
+  const run = battle.run();
+  let input: BattleInput;
+  for (let step = 0; step < 3000; step++) {
+    const next = run.next(input);
+    if (next.done) return { texts, prompts, result: next.value.result };
+    const effect = next.value;
+    input = undefined;
+    if (effect.kind === "text") texts.push(effect.text.replace(/\n/g, " "));
+    else if (effect.kind !== "hud") {
+      prompts.push(effect);
+      const answer = queued[effect.kind]?.shift();
+      input =
+        answer !== undefined
+          ? answer
+          : effect.kind === "action"
+            ? { action: "fight", move: 0 }
+            : effect.kind === "yesno"
+              ? 1
+              : effect.kind === "forget"
+                ? 4
+                : effect.kind === "party"
+                  ? 0
+                  : undefined;
+    }
+  }
+  throw new Error("Battle did not end.");
+}