Port Headbutt and Rock Smash encounters

Facing a Headbutt tree asks to HEADBUTT it, and HEADBUTT from the party
menu skips the question. ShakeHeadbuttTree shakes the tree as a sprite over
grass, then TreeMonEncounter scores the facing tile against the trainer ID
and draws from the map's common or rare tree table. A Pokémon that falls
fights as BATTLETYPE_TREE: "fell out of the tree!", and the time of day's
AsleepTreeMons species start asleep.

Smashable rocks run SmashRockScript, and ROCK SMASH from the party menu
acts on the facing rock; after the rock breaks, RockMonEncounter gives the
map's rock set a 40% chance of a wild battle.

Closes #26

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

src/game/scripts/start-menu.ts

@@ -96,6 +96,8 @@ export type MenuFieldMove =
       script: number;
       fieldMove: FieldMoveContext;
       wild?: { species: number; level: number };
+      /** hLastTalked, when the move acts on a facing object. */
+      lastTalked?: number;
     }
   | { texts: number[] }
   | { notice: string }