Fix fall-through (spawn on terrain after collision built) and B&W (assign sky env)

scripts/world/world.gd

@@ -0,0 +1,31 @@
+extends Node3D
+## World controller — M0.
+##
+## Owns spawn ordering so the player never falls through ungenerated ground:
+## waits for the terrain to finish building, then drops the player onto the
+## surface height and lets gravity settle them. Also tells the props where the
+## ground is so they sit on it instead of floating.
+
+@onready var terrain: Node3D = $Terrain
+@onready var props: Node3D = $Props
+@onready var player: CharacterBody3D = $Player
+
+func _ready() -> void:
+	# Freeze the player until the ground exists.
+	player.set_physics_process(false)
+	if terrain.built:
+		_on_terrain_ready()
+	else:
+		terrain.ready_built.connect(_on_terrain_ready)
+
+func _on_terrain_ready() -> void:
+	# Let props place themselves on the surface.
+	if props.has_method("place_on"):
+		props.place_on(terrain)
+
+	# Spawn the player on the ground at (0,0), a little above so they settle down
+	# onto the collision rather than starting embedded in it.
+	var h: float = terrain.sample_height(0.0, 0.0)
+	player.global_position = Vector3(0.0, h + 2.0, 0.0)
+	player.velocity = Vector3.ZERO
+	player.set_physics_process(true)