feat(theme): parchment/dark-bay/vignette shader surfaces as drop-in scenes

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/scripts/theme/surfaces/vignette_overlay.gd

@@ -0,0 +1,11 @@
+class_name VignetteOverlay
+extends ColorRect
+## Drop-in edge-dim overlay for pause/dialogue dim. §2: presentation.
+
+
+func _ready() -> void:
+	color = Color(0, 0, 0, 0)  # base transparent; shader draws the dim
+	mouse_filter = Control.MOUSE_FILTER_IGNORE
+	var m := ShaderMaterial.new()
+	m.shader = load("res://assets/theme/shaders/vignette.gdshader")
+	material = m