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/battle/battle.ts

@@ -175,6 +175,8 @@ export interface BattleOptions {
   caughtData?: (level: number) => number;
   /** BATTLETYPE_TUTORIAL: the Dude's catching demonstration. */
   tutorial?: boolean;
+  /** BATTLETYPE_TREE: a wild Pokémon that fell from a Headbutt tree. */
+  tree?: boolean;
   /** GetWorldMapLocation for the current map (LevelUpHappinessMod). */
   landmark?: number;
   /** wPartyMenuCursor as the last party menu outside battle left it. */
@@ -476,6 +478,7 @@ export class Battle {
     this.partyMenuCursor = options.partyMenuCursor ?? 0;
     if (options.trainer) this.battleMode = C.TRAINER_BATTLE;
     if (options.tutorial) this.battleType = C.BATTLETYPE_TUTORIAL;
+    else if (options.tree) this.battleType = C.BATTLETYPE_TREE;
   }
   private get reader(): RomReader {
     return this.options.data.reader;
@@ -659,7 +662,8 @@ export class Battle {
       pp: moves.map((move) => (move ? data.move(move).pp : 0)),
       happiness: C.BASE_HAPPINESS,
       level,
-      status: 0,
+      // .TreeMon: some Pokémon fall from trees asleep.
+      status: this.sleepingTreeMon(species) ? C.TREEMON_SLEEP_TURNS : 0,
       hp: stats[0],
       maxHp: stats[0],
       stats: stats.slice(1),
@@ -676,6 +680,21 @@ export class Battle {
     this.wildMoves = [...moves];
     this.wildPP = [...this.enemy.mon.pp];
   }
+  /** CheckSleepingTreeMon: in a tree battle, the time of day's
+   * AsleepTreeMons list names the species that sleep. */
+  private sleepingTreeMon(species: number) {
+    if (this.battleType !== C.BATTLETYPE_TREE) return false;
+    const time = this.options.timeOfDay;
+    let p =
+      time < C.DAY_F
+        ? BATTLE.AsleepTreeMonsMorn
+        : time === C.DAY_F
+          ? BATTLE.AsleepTreeMonsDay
+          : BATTLE.AsleepTreeMonsNite;
+    for (const r = this.reader; r.byte(p) !== 0xff; p++)
+      if (r.byte(p) === species) return true;
+    return false;
+  }
   /** InitBattleMon from the party, then status penalties. */
   private initBattleMon() {
     const mon = this.partyMon,
@@ -773,7 +792,12 @@ export class Battle {
     if (trainer) {
       yield* this.say(BATTLE.WantsToBattleText);
       yield* this.say(BATTLE.BattleText_EnemySentOut);
-    } else yield* this.say(BATTLE.WildPokemonAppearedText);
+    } else
+      yield* this.say(
+        this.battleType === C.BATTLETYPE_TREE
+          ? BATTLE.PokemonFellFromTreeText
+          : BATTLE.WildPokemonAppearedText,
+      );
     this.resetBattleParticipants();
     this.initBattleMon();
     const amuletCoin =