P14-02: Split warps into guest FRONT and staff BACK service warp (A08)

The FRONT Mana warp is guest-only: its connectors carry the "!staff" access,
which path access checks treat as open to everyone except staff. A new 2x2
BACK service warp links only to other service warps for staff, with A07
values. Registry and palette now hold 25 definitions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/ui/pixel_tower_art.gd

@@ -89,7 +89,7 @@ static func room(canvas: CanvasItem, rect: Rect2, id: StringName, pixel: float,
 				table(canvas, at + Vector2(-2, -7)*p, p)
 		&"chapel":
 			chapel_furnishings(canvas, rect, p)
-		&"mana_warp":
+		&"mana_warp", &"service_warp":
 			# Original code-drawn transfer circle and rising motes; existing palette.
 			var ring := Vector2(mid, floor_y - 3.0 * p)
 			canvas.draw_circle(ring, 9.0 * p, INK)