Port field moves from the menu, SEL with Select, and moving Pokémon in Bill's PC

Field moves chosen in the party menu run their original checks and the
ROM's from-menu scripts (Cut, Surf, Strength, Flash, Whirlpool, Waterfall,
Sweet Scent), and Softboiled and Milk Drink share HP. SEL registers a key
item that Select then uses, replacing the Key Items shortcut, and Bill's
PC moves Pokémon between the party and every box.

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

src/game/scripts/text.ts

@@ -85,7 +85,7 @@ export interface TextContext {
   battle?: { turn: number; player: string; enemy: string; enemyPrefix: string };
   /** Native handlers for text_asm, keyed by the command's ROM offset. They
    * return where text continues, as the original routine returns in hl. */
-  asm?: (offset: number) => number;
+  asm?: (offset: number) => number | undefined;
 }
 
 export const defaultTextContext = (player: string): TextContext => ({