Add explicit stairs and measure elevator congestion with real actors

scripts/data/facility_catalog.gd

@@ -44,6 +44,18 @@ const FACILITY_PATHS: Array[String] = [
 	"res://data/facilities/adult_private_room.tres",
 ]
 
+## Required movement infrastructure added after the original sixteen-facility
+## catalog. Separate paths preserve the baseline design table and legacy scans.
+const INFRASTRUCTURE_FACILITY_IDS: Array[StringName] = [
+	&"guest_stairs",
+	&"service_stairs",
+]
+
+const INFRASTRUCTURE_FACILITY_PATHS: Array[String] = [
+	"res://data/facilities/infrastructure/guest_stairs.tres",
+	"res://data/facilities/infrastructure/service_stairs.tres",
+]
+
 ## Optional post-MVP expansion definitions. They live below a subdirectory so
 ## DefinitionRegistry's baseline directory scan remains exactly compatible with
 ## existing saves and the sixteen-facility acceptance fixture.
@@ -101,6 +113,14 @@ static func load_expansion() -> Array[FacilityDefinition]:
 			result.append(definition)
 	return result
 
+static func load_infrastructure() -> Array[FacilityDefinition]:
+	var result: Array[FacilityDefinition] = []
+	for path in INFRASTRUCTURE_FACILITY_PATHS:
+		var definition := load(path) as FacilityDefinition
+		if definition != null:
+			result.append(definition)
+	return result
+
 static func load_available(include_expansion := false) -> Array[FacilityDefinition]:
 	var result := load_all()
 	if include_expansion:
@@ -108,7 +128,9 @@ static func load_available(include_expansion := false) -> Array[FacilityDefiniti
 	return result
 
 static func by_id(facility_id: StringName) -> FacilityDefinition:
-	for definition in load_available(true):
+	var definitions := load_available(true)
+	definitions.append_array(load_infrastructure())
+	for definition in definitions:
 		if definition.id == facility_id:
 			return definition
 	return null