Add hazard spikes on the tree tops (grey spikes from the tileset atlas)

The two new spikes were painted as tiles in TerrainBase, but tileset collision can only make a solid wall, not a damaging hazard. Replaced them with a real spikes_grey prefab that uses the same atlas tile (8,3) plus hazard.gd, and erases the placeholder tile on ready. Also includes the level edits made in the editor (top-left terrain rework).

scripts/hazard.gd

@@ -1,14 +1,29 @@
 extends Area2D
 
-## 尖刺：碰到就把角色打回出生点。
+## 尖刺：碰到就把角色打回出生点、扣一颗心。
 ## 碰撞掩码已经限制成只检测玩家那一层，所以进到这里的一定是玩家。
 @export var damage: int = 1
+## 开场时把自己脚下那块占位地砖擦掉
+## （关卡里有些尖刺是直接画在地砖上的，换成真正的尖刺对象后要把它擦掉，避免重叠）
+@export var erase_placeholder_tile: bool = false
 
 
 func _ready() -> void:
 	body_entered.connect(_on_body_entered)
+	if erase_placeholder_tile:
+		_erase_placeholder_tile()
 
 
 func _on_body_entered(body: Node2D) -> void:
 	if body.has_method("hurt"):
 		body.hurt(damage)
+
+
+func _erase_placeholder_tile() -> void:
+	var root: Node = owner if owner != null else get_parent()
+	if root == null:
+		return
+	for layer in root.find_children("*", "TileMapLayer", true, false):
+		var cell: Vector2i = layer.local_to_map(layer.to_local(global_position))
+		if layer.get_cell_source_id(cell) != -1:
+			layer.erase_cell(cell)