Buy fleet berths with Fleet Offices

#219: fleet capacity is a built, supplied thing rather than a researched
one. The eight fleet-size doctrines are gone; capacity is one berth free
plus one per Fleet Office standing. An office charges every 25s for the
vessel in its berth, priced off that vessel's own build cost so an expensive
hull is expensive to keep, and drawn from its own store the way a gas burner
draws gas. An office that cannot pay goes dark, its vessel is scuttled, and
the player is told through the same queue quest lines use - which reaches
them on a planet surface too.

An empty berth is idle rather than starved: an office is only failing while
there is something in it to fail, and holding it disabled would leave a
berth that could never be crewed and so could never be paid for again.

Ships have no hit points and a shield absorbs a hit wholesale, so the lost
vessel is scuttled rather than damaged - otherwise a shielded hull would
survive its own eviction.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019AJMdB7iuHuLFZM1aBu3GD

tests/test_enemy_collision.gd

@@ -22,6 +22,10 @@ var started: bool = false
 
 
 func _initialize() -> void:
+	# #219: fleet capacity is built now - one berth free, one per Fleet
+	# Office. This test flies more than one vessel, so it needs the offices
+	# standing before the fleet spawns into them.
+	load("res://tests/_berths.gd").grant(root.get_node("GameState"), 6)
 	var packed: PackedScene = load("res://world/Main.tscn")
 	main_scene = packed.instantiate()
 	root.add_child(main_scene)
@@ -42,7 +46,6 @@ func _physics_process(delta: float) -> bool:
 		# can be undone by the engine's deferred tree-entry finalization. A
 		# new game flies one vessel into three slots now, and this test needs
 		# a full one.
-		root.get_node("GameState").unlocked.append_array(["wing", "squadron", "armada"])
 		fleet.spawn_ships(5, Vector2.ZERO)
 		target_ship = fleet.ships[0]
 		var enemy_scene: PackedScene = load("res://enemies/Enemy.tscn")