Fix washed-out look (inverted terrain normals via winding), tune lighting/fog, add tree+rock collision

scripts/world/props.gd

@@ -36,6 +36,17 @@ func _make_tree(pos: Vector3, rng: RandomNumberGenerator) -> void:
 	trunk.material_override = _mat(Color(0.33, 0.24, 0.16))
 	root.add_child(trunk)
 
+	# Collision: a capsule around the trunk so you can't walk through the tree.
+	var body := StaticBody3D.new()
+	root.add_child(body)
+	var col := CollisionShape3D.new()
+	var cap := CapsuleShape3D.new()
+	cap.radius = 0.35
+	cap.height = 4.0
+	col.shape = cap
+	col.position = Vector3(0, 2.0, 0)
+	body.add_child(col)
+
 	# Low-poly conifer canopy: stacked cones.
 	var h := 3.0
 	for j in range(3):
@@ -57,13 +68,25 @@ func _make_tree(pos: Vector3, rng: RandomNumberGenerator) -> void:
 func _make_rock(pos: Vector3, rng: RandomNumberGenerator) -> void:
 	var rock := MeshInstance3D.new()
 	var bm := BoxMesh.new()
-	bm.size = Vector3(rng.randf_range(0.8, 1.8), rng.randf_range(0.6, 1.2), rng.randf_range(0.8, 1.8))
+	var box_size := Vector3(rng.randf_range(0.8, 1.8), rng.randf_range(0.6, 1.2), rng.randf_range(0.8, 1.8))
+	bm.size = box_size
 	rock.mesh = bm
 	rock.position = pos + Vector3(0, 0.3, 0)
 	rock.rotation = Vector3(rng.randf_range(-0.2, 0.2), rng.randf_range(0, TAU), rng.randf_range(-0.2, 0.2))
 	rock.material_override = _mat(Color(0.42, 0.42, 0.45))
 	add_child(rock)
 
+	# Collision: a box matching the rock mesh.
+	var body := StaticBody3D.new()
+	body.position = rock.position
+	body.rotation = rock.rotation
+	add_child(body)
+	var col := CollisionShape3D.new()
+	var box := BoxShape3D.new()
+	box.size = box_size
+	col.shape = box
+	body.add_child(col)
+
 func _mat(c: Color) -> StandardMaterial3D:
 	var m := StandardMaterial3D.new()
 	m.albedo_color = c