Tune and optimize boss encounter

surface/PlanetSurfaceProfile.gd

@@ -17,6 +17,10 @@ extends Resource
 # the game and the setup editor drift apart, since each scene "already had" a
 # different shader. SurfaceBackground.apply_profile() is the only consumer.
 @export var background_shader: Shader = null
+# Optional ready-made field for a tiled background shader. Procedural rocky
+# terrain still bakes once; authored surfaces can avoid both that load spike
+# and all per-frame procedural fragment work by shipping their tile directly.
+@export var background_field_texture: Texture2D = null
 @export var base_color: Color = Color(0.75, 0.75, 0.76, 1.0)
 @export var crater_color: Color = Color(0.44, 0.44, 0.45, 1.0)
 @export var highlight_color: Color = Color(0.89, 0.89, 0.9, 1.0)