Port the start menu, the party menu and the pack outside battle

Start opens the original start menu. POKéMON shows the party with the
Pokémon submenu (stats, switching, move order, held items); PACK shows the
four pockets with the field item effects for healing, PP and the Bicycle,
plus giving and tossing. The menu runs on a script draft, and its cursors
persist until a battle clears them. Select keeps the Key Items shortcut.

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

src/game/battle/constants.ts

@@ -239,6 +239,26 @@ export const C = {
   BATTLEPLAYERACTION_SWITCH: 2,
   ITEMMENU_CURRENT: 4,
   ITEMMENU_PARTY: 5,
+  ITEMMENU_CLOSE: 6,
+  // Menus outside battle (constants/menu_constants.asm)
+  MONMENU_FIELD_MOVE: 0,
+  MONMENUITEM_STATS: 15,
+  MONMENUITEM_SWITCH: 16,
+  MONMENUITEM_ITEM: 17,
+  MONMENUITEM_CANCEL: 18,
+  MONMENUITEM_MOVE: 19,
+  MONMENUITEM_MAIL: 20,
+  NUM_MONMENU_ITEMS: 8,
+  PARTYMENUACTION_CHOOSE_POKEMON: 0,
+  PARTYMENUACTION_HEALING_ITEM: 1,
+  PARTYMENUACTION_MOVE: 4,
+  PARTYMENUACTION_GIVE_ITEM: 8,
+  KEY_ITEM_POCKET: 2,
+  TM_HM_POCKET: 3,
+  PP_UP: 0x3e,
+  SKETCH: 0xa6,
+  PP_UP_MASK: 0xc0,
+  PP_UP_ONE: 0x40,
   PARTYMENUTEXT_HEAL_HP: 0xf5,
   PARTYMENUTEXT_HEAL_CONFUSION: 0xf9,
   PARTYMENUTEXT_REVIVE: 0xf7,