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>

src/game/world/world.ts

@@ -241,7 +241,7 @@ export interface BattleView {
   /** A choice the battle is waiting for, if any. */
   prompt?: Extract<
     BattleEffect,
-    { kind: "action" | "yesno" | "forget" | "stats" | "name" }
+    { kind: "action" | "yesno" | "forget" | "stats" | "name" | "party" }
   >;
   /** Yes/No cursor, as on the original boxes. */
   selected: 0 | 1;
@@ -2346,10 +2346,15 @@ export class GameWorld {
       return;
     this.pumpBattle(name);
   }
-  /** Answer a battle Yes/No (1/0) or the move to forget (0-3, 4 cancels). */
+  /** Answer a battle Yes/No (1/0), the move to forget (0-3, 4 cancels)
+   * or a party menu (a party index, or -1 to go back). */
   battleChoose(answer: number) {
     const prompt = this.battle?.prompt;
-    if (prompt?.kind === "yesno" || prompt?.kind === "forget")
+    if (
+      prompt?.kind === "yesno" ||
+      prompt?.kind === "forget" ||
+      prompt?.kind === "party"
+    )
       this.pumpBattle(answer);
   }
   /** A in battle: continue a prompt message, confirm Yes/No or the stat box. */
@@ -2366,6 +2371,7 @@ export class GameWorld {
     const prompt = view.prompt;
     if (prompt?.kind === "yesno") return this.pumpBattle(0);
     if (prompt?.kind === "forget") return this.pumpBattle(4);
+    if (prompt?.kind === "party" && prompt.cancel) return this.pumpBattle(-1);
     if (prompt?.kind === "stats") return this.pumpBattle();
     if (!prompt && view.message?.prompt) this.pumpBattle();
   }