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/rom/assets.ts

@@ -500,6 +500,10 @@ export class CrystalAssets {
       r.byte(entry + 2),
     );
   }
+  /** HeadbuttTreeGFX: the shaking tree's two 2x2 frames, eight tiles. */
+  headbuttTree(): Uint8Array {
+    return this.reader.slice(OVERWORLD.HeadbuttTreeGFX, 8 * 16);
+  }
   /** GetIcon: a species' two-frame party menu icon (ReadMonMenuIcon and
    * IconPointers), eight tiles. */
   monIcon(species: number): Uint8Array {

src/game/rom/profile.ts

@@ -159,6 +159,7 @@ export const RAM = {
   strengthSpecies: 0xd1ef,
   curHPAnimDeltaHP: 0xd1f3,
   visitedSpawns: 0xdca5,
+  tempWildMonSpecies: 0xd22e,
   /** hMoneyTemp: HRAM, not WRAM like the other entries above. */
   moneyTemp: 0xffc3,
 } as const;
@@ -233,6 +234,17 @@ export const OVERWORLD = {
   Script_WaterfallFromMenu: 0xcb1c,
   "SweetScentFromMenu.SweetScent": 0x506c8,
   SweetScentEncounter: 0x506ef,
+  HeadbuttFromMenuScript: 0xcea7,
+  AskHeadbuttScript: 0xcedc,
+  ShakeHeadbuttTree: 0x8c80a,
+  HeadbuttTreeGFX: 0x8c893,
+  TreeMonEncounter: 0xb81ea,
+  RockMonEncounter: 0xb8219,
+  TreeMonMaps: 0xb825e,
+  RockMonMaps: 0xb82c5,
+  TreeMons: 0xb82e8,
+  RockSmashFromMenuScript: 0xcf2e,
+  HasRockSmash: 0xcf7c,
   "CheckBadge.BadgeRequiredText": 0xc73d,
   "FieldMoveFailed.CantUseItemText": 0xc780,
   CutNothingText: 0xc7c9,
@@ -685,6 +697,10 @@ export const BATTLE = {
   WasBurnedText: 0x8123c,
   WasPoisonedText: 0x811d5,
   WildPokemonAppearedText: 0x80746,
+  PokemonFellFromTreeText: 0x80778,
+  AsleepTreeMonsNite: 0x3eb5d,
+  AsleepTreeMonsDay: 0x3eb69,
+  AsleepTreeMonsMorn: 0x3eb6f,
   WokeUpText: 0x80cfa,
   WontDropAnymoreText: 0x8128f,
   WontRiseAnymoreText: 0x81272,