Typed owed vessels, ship lab building type, shield vessel gate

Groundwork for #5. vessels_owed carries the VESSEL TYPE rather than a
bare count, so a shield vessel finishing while the player is on a planet
comes back as a shield vessel. Fleet.add_ship takes a type, and vessels
already flying are re-statted when an upgrade is researched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_crafter_feedback.gd

@@ -38,7 +38,7 @@ func _initialize() -> void:
 	game_state.unlocked = ["shipyards", "coordination", "wing"]
 	game_state.rocks = 100
 	game_state.fleet_cargo = 0
-	game_state.ships_owed = 0
+	game_state.vessels_owed.clear()
 	scene = load("res://Main.tscn").instantiate()
 	root.add_child(scene)
 	controller = scene.get_node("BuildController")