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/battle/constants.ts

@@ -236,6 +236,12 @@ export const C = {
 
   // Battle modes, types and results
   BATTLEPLAYERACTION_USEITEM: 1,
+  BATTLEPLAYERACTION_SWITCH: 2,
+  ITEMMENU_CURRENT: 4,
+  ITEMMENU_PARTY: 5,
+  PARTYMENUTEXT_HEAL_HP: 0xf5,
+  PARTYMENUTEXT_HEAL_CONFUSION: 0xf9,
+  EGG: 0xfd,
   WILD_BATTLE: 1,
   TRAINER_BATTLE: 2,
   HELD_AMULET_COIN: 76,