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/assets/theme/shaders/dark_bay.gdshader

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+shader_type canvas_item;
+uniform vec4 stripe_a : source_color;
+uniform vec4 stripe_b : source_color;
+uniform float band_px = 16.0;    // 16px bands per README
+uniform float vignette = 0.55;   // edge darkening strength
+void fragment() {
+	// 135deg diagonal stripe: sum of pixel coords, banded.
+	vec2 px = FRAGCOORD.xy;
+	float diag = px.x + px.y;
+	float band = mod(floor(diag / band_px), 2.0);
+	vec4 base = mix(stripe_a, stripe_b, band);
+	// radial vignette centred slightly high (README: 50% 38%).
+	float d = distance(UV, vec2(0.5, 0.38));
+	base.rgb *= 1.0 - clamp(d * vignette, 0.0, 1.0);
+	COLOR = base;
+}

client/assets/theme/shaders/dark_bay.gdshader.uid

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+uid://jb8clyworwr1

client/assets/theme/shaders/parchment.gdshader

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+shader_type canvas_item;
+uniform vec4 top : source_color;
+uniform vec4 bottom : source_color;
+void fragment() {
+	COLOR = mix(top, bottom, UV.y);
+}

client/assets/theme/shaders/parchment.gdshader.uid

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+uid://b2heb6jhvwxxl

client/assets/theme/shaders/vignette.gdshader

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+shader_type canvas_item;
+uniform float strength = 0.62;
+void fragment() {
+	float d = distance(UV, vec2(0.5));
+	COLOR = vec4(0.0, 0.0, 0.0, clamp(d * strength, 0.0, 1.0));
+}

client/assets/theme/shaders/vignette.gdshader.uid

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+uid://b4tami4peyxaw

client/scenes/theme/surfaces/DarkBay.tscn

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+[gd_scene load_steps=2 format=3]
+[ext_resource type="Script" path="res://scripts/theme/surfaces/dark_bay.gd" id="1"]
+[node name="DarkBay" type="Panel"]
+anchors_preset = 15
+script = ExtResource("1")

client/scenes/theme/surfaces/ParchmentPanel.tscn

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+[gd_scene load_steps=2 format=3]
+[ext_resource type="Script" path="res://scripts/theme/surfaces/parchment_panel.gd" id="1"]
+[node name="ParchmentPanel" type="Panel"]
+anchors_preset = 15
+script = ExtResource("1")

client/scenes/theme/surfaces/VignetteOverlay.tscn

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+[gd_scene load_steps=2 format=3]
+[ext_resource type="Script" path="res://scripts/theme/surfaces/vignette_overlay.gd" id="1"]
+[node name="VignetteOverlay" type="ColorRect"]
+anchors_preset = 15
+script = ExtResource("1")

client/scripts/theme/surfaces/dark_bay.gd

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+class_name DarkBay
+extends Panel
+## Drop-in dark stripe+vignette bay backdrop. §2: presentation.
+const Palette = preload("res://scripts/theme/palette.gd")
+
+
+func _ready() -> void:
+	var m := ShaderMaterial.new()
+	m.shader = load("res://assets/theme/shaders/dark_bay.gdshader")
+	m.set_shader_parameter("stripe_a", Palette.BAY_STRIPE_A)
+	m.set_shader_parameter("stripe_b", Palette.BAY_STRIPE_B)
+	material = m

client/scripts/theme/surfaces/dark_bay.gd.uid

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+uid://24c8pl0yx8wu

client/scripts/theme/surfaces/parchment_panel.gd

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+class_name ParchmentPanel
+extends Panel
+## Drop-in parchment backdrop (mockups "Dark Bay + Parchment" motif). §2: presentation.
+const Palette = preload("res://scripts/theme/palette.gd")
+
+
+func _ready() -> void:
+	var m := ShaderMaterial.new()
+	m.shader = load("res://assets/theme/shaders/parchment.gdshader")
+	m.set_shader_parameter("top", Palette.SHEET_TOP)
+	m.set_shader_parameter("bottom", Palette.SHEET_BOTTOM)
+	material = m

client/scripts/theme/surfaces/parchment_panel.gd.uid

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+uid://cnv1r00ane2la

client/scripts/theme/surfaces/vignette_overlay.gd

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+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

client/scripts/theme/surfaces/vignette_overlay.gd.uid

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+uid://7bc7agrl6oi0

client/tests/unit/test_surfaces.gd

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+extends "res://addons/gut/test.gd"
+
+const SCENES := [
+	"res://scenes/theme/surfaces/ParchmentPanel.tscn",
+	"res://scenes/theme/surfaces/DarkBay.tscn",
+	"res://scenes/theme/surfaces/VignetteOverlay.tscn",
+]
+
+
+func test_surfaces_instance_with_shader_material():
+	for path in SCENES:
+		var packed = load(path)
+		assert_true(packed is PackedScene, "not a scene: %s" % path)
+		var node = packed.instantiate()
+		add_child_autofree(node)   # triggers _ready()
+		assert_true(node.material is ShaderMaterial, "%s has no ShaderMaterial" % path)
+		assert_true(node.material.shader is Shader, "%s shader missing" % path)

client/tests/unit/test_surfaces.gd.uid

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+uid://csc3r7lqoe83d