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>

tests/foundation-fixture.ts

@@ -9,10 +9,21 @@ import { generatePartyMon } from "../src/game/party/pokemon";
  * Pokégear, its map and phone cards, and Mom's and Elm's numbers). "mom"
  * faces Mom in the living room after the Mystery Egg, with her bank open
  * and ¥2300 saved. "fly" stands outdoors with a Pidgeot that knows Fly,
- * the Storm Badge, and New Bark Town and Cherrygrove City visited. */
+ * the Storm Badge, and New Bark Town and Cherrygrove City visited.
+ * "headbutt" faces Route 29's first reachable Headbutt tree from below
+ * with a Pokémon that knows Headbutt; Random always returning 0 drops a
+ * sleeping Hoothoot. */
 export function foundationFixture(
   assets: CrystalAssets,
-  room: boolean | "poster" | "center" | "candy" | "pokegear" | "mom" | "fly",
+  room:
+    | boolean
+    | "poster"
+    | "center"
+    | "candy"
+    | "pokegear"
+    | "mom"
+    | "fly"
+    | "headbutt",
 ) {
   const world = new GameWorld(
     assets,
@@ -73,6 +84,21 @@ export function foundationFixture(
       world.state.flags.add(assets.spawnEngineFlag(spawn)!);
     for (let event = 0; event < 8; event++) world.state.events.delete(event);
   }
+  if (room === "headbutt") {
+    const mon = generatePartyMon(assets.pokemon, {
+      species: 158, // TOTODILE
+      level: 30,
+      item: 0,
+      otId: world.playerId,
+      ot: "CHRIS",
+      dvs: 0x9abc,
+      caughtData: 0,
+    });
+    mon.moves = [OW.HEADBUTT, 33, 0, 0]; // TACKLE
+    mon.pp = [15, 35, 0, 0];
+    world.state.party = [mon];
+    for (let event = 0; event < 8; event++) world.state.events.delete(event);
+  }
   if (room === "mom") {
     // EVENT_GOT_MYSTERY_EGG_FROM_MR_POKEMON, EVENT_GAVE_MYSTERY_EGG_TO_ELM
     // and EVENT_TALKED_TO_MOM_AFTER_MYSTERY_EGG_QUEST.
@@ -83,15 +109,17 @@ export function foundationFixture(
   }
   const save = world.save();
   const [map, x, y] =
-    room === "center" || room === "candy"
-      ? ["26:5", 9, 2]
-      : room === "poster"
-        ? ["24:7", 6, 1]
-        : room === "mom"
-          ? ["24:6", 7, 3]
-          : room && room !== "pokegear" && room !== "fly"
-            ? ["24:7", 2, 2]
-            : ["24:4", 9, 6];
+    room === "headbutt"
+      ? headbuttSpot(assets)
+      : room === "center" || room === "candy"
+        ? ["26:5", 9, 2]
+        : room === "poster"
+          ? ["24:7", 6, 1]
+          : room === "mom"
+            ? ["24:6", 7, 3]
+            : room && room !== "pokegear" && room !== "fly"
+              ? ["24:7", 2, 2]
+              : ["24:4", 9, 6];
   world.restore({
     ...save,
     map,
@@ -102,3 +130,17 @@ export function foundationFixture(
   });
   return world;
 }
+
+/** Below Route 29's first Headbutt tree with walkable ground under it. */
+function headbuttSpot(assets: CrystalAssets): [string, number, number] {
+  const map = assets.map("24:3");
+  for (let y = 1; y < map.height - 1; y++)
+    for (let x = 0; x < map.width; x++)
+      if (
+        assets.collision(map, x, y) === OW.COLL_HEADBUTT_TREE &&
+        assets.permission(assets.collision(map, x, y + 1)) === 0 &&
+        !map.objects.some((o) => o.x === x && o.y <= y + 1 && o.y >= y)
+      )
+        return ["24:3", x, y + 1];
+  throw new Error("No reachable Headbutt tree.");
+}