Add planet setups as authored resources (#42)

PlanetSetup/PlanetSetupSpawn define a curated capture-point/enemy
layout for a surface profile; PlanetSetups scans res://PlanetSetups/
at first use (not a hardcoded preload table) so dropping in a new
.tres is the only step needed to add one, and resolves the same
setup for the same planet deterministically, same pattern as
WorldGen.planet_data_at_chunk. PlanetSurfaceController composes a
PlanetSetupHost onto the landed surface alongside the existing
resource-provider feature scene.

Ships two starter setups (rocky_default, gas_default) with
placeholder capture-point markers; #43 replaces the markers with the
real CapturePoint scene through the same apply_setup() entry point.

Part of the #40 conquest-mechanic breakdown.

PlanetSetupHost.gd

@@ -0,0 +1,33 @@
+class_name PlanetSetupHost
+extends Node2D
+
+# Instantiates the contents of a PlanetSetup onto a landed surface. Capture
+# points are placeholder markers here; #43 replaces them with the real
+# CapturePoint scene through the same apply_setup() entry point, and enemy
+# spawning is filled in by the enemy-foundation ticket (#44). Keeping this
+# seam stable is the point of this ticket.
+
+const MARKER_COLOR: Color = Color(0.55, 0.85, 1.0)
+const MARKER_RADIUS: float = 36.0
+
+var setup: Resource
+
+
+func apply_setup(new_setup: Resource) -> void:
+	setup = new_setup
+	for child in get_children():
+		child.queue_free()
+	if setup == null:
+		return
+	for point in setup.capture_points:
+		_add_capture_point_marker(point)
+
+
+func _add_capture_point_marker(at: Vector2) -> void:
+	var marker: NeonPiece = NeonPiece.create(self, at, MARKER_COLOR)
+	var points: PackedVector2Array = PackedVector2Array()
+	for i in range(16):
+		var angle: float = float(i) / 16.0 * TAU
+		points.append(Vector2(cos(angle), sin(angle)) * MARKER_RADIUS)
+	marker.add_polygon(points, 0.6)
+	marker.queue_redraw()