Expand and stage boss encounter

tests/_boss_approach_preview.gd

@@ -0,0 +1,25 @@
+extends Node2D
+
+# Stable portrait view of #189's pre-fight state: the landed fleet is still
+# below the unseen Warden, combat HUD is absent, and only the edge indicator
+# gives away what is pulling the fleet upward.
+
+
+func _ready() -> void:
+	GameState.reset_new_game()
+	GameState.intro_active = false
+	GameState.reset_quests(false)
+	GameState.planet_name = "Many-Eyed Deep"
+	GameState.planet_id = "preview:boss:approach"
+	GameState.planet_definition_id = "boss"
+	GameState.surviving_ship_count = 3
+	GameState.surviving_vessel_types = PackedStringArray([
+		GameState.VESSEL_INTERCEPTOR,
+		GameState.VESSEL_GAS_BOMBER,
+		GameState.VESSEL_LASER,
+	])
+	var surface: Node = load("res://surface/PlanetSurface.tscn").instantiate()
+	add_child(surface)
+	surface.get_node("FadeOverlay/FadeRect").visible = false
+	# Four screenshot frames are nowhere near enough for the automatic
+	# approach to cover 950 world units, so the signal remains off-screen.