feat(sites): typed dive site definition with placements and routes

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

game/domain/sites/terrain_height_field.gd

@@ -12,7 +12,8 @@ var _maximum_elevation_m := 0.0
 static func from_data(data: SiteTerrainData) -> TerrainHeightField:
 	if data == null or not data.validation_error().is_empty():
 		return null
-	var field := TerrainHeightField.new()
+	var script_class = load("res://game/domain/sites/terrain_height_field.gd")
+	var field: TerrainHeightField = script_class.new()
 	field._data = data
 	field._minimum_elevation_m = data.elevations_m[0]
 	field._maximum_elevation_m = data.elevations_m[0]