feat(@projects/@magic-civilization): ✨ add hybrid merge proof scene test

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/game/engine/scenes/tests/proof_hybrid_merge.gd

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+extends Node
+## p1-59 Proof Scene — Hybrid Merged Structures.
+## Proves: merge_panel.gd can be populated with a city that has
+## rifle_range + barding_hall (prereq pair for war_academy), and the
+## merge panel shows the "war_academy" row. A tech-gated row (gunnery_corps)
+## is shown greyed out (military_synthesis not in researched_techs).
+## Captures a screenshot and quits.
+
+const MergePanelScene: PackedScene = preload(
+	"res://engine/scenes/city/merge_panel.tscn"
+)
+
+var _captured: bool = false
+var _screenshot_name: String = "p1_59_hybrid_merge_proof"
+var _label_root: VBoxContainer
+var _merge_panel: PanelContainer
+
+
+## Minimal fake GdCity bridge that mocks available_merges().
+class FakeGdCity:
+	func call_method(method: String, _registry_json: String, _researched_techs: PackedStringArray) -> Array:
+		if method == "available_merges":
+			return [
+				{
+					"building_a": "rifle_range",
+					"building_b": "barding_hall",
+					"into": "war_academy",
+					"tech_gated": false,
+				},
+				{
+					"building_a": "rifle_range",
+					"building_b": "powder_annex",
+					"into": "gunnery_corps",
+					"tech_gated": true,
+				},
+			]
+		return []
+
+
+class FakeBridge:
+	var _gd_city: FakeGdCity = FakeGdCity.new()
+
+	func is_available() -> bool:
+		return true
+
+
+class FakeCity:
+	var _bridge: FakeBridge = FakeBridge.new()
+	var id: String = "proof_city"
+	var buildings: Array = ["rifle_range", "barding_hall", "powder_annex"]
+
+
+func _ready() -> void:
+	RenderingServer.set_default_clear_color(Color(0.06, 0.05, 0.04))
+	get_tree().root.size = Vector2i(1280, 720)
+	_build_ui()
+	await get_tree().process_frame
+	await get_tree().process_frame
+	_show_merge_panel()
+	await get_tree().process_frame
+	_capture()
+
+
+func _build_ui() -> void:
+	var bg: ColorRect = ColorRect.new()
+	bg.anchors_preset = Control.PRESET_FULL_RECT
+	bg.color = Color(0.08, 0.07, 0.06)
+	add_child(bg)
+
+	_label_root = VBoxContainer.new()
+	_label_root.set_anchors_and_offsets_preset(Control.PRESET_TOP_LEFT)
+	_label_root.position = Vector2(24.0, 24.0)
+	add_child(_label_root)
+
+	_add_label("p1-59 Proof — Hybrid Merged Structures", 20, Color(0.95, 0.85, 0.45))
+	_add_label("City has: rifle_range, barding_hall, powder_annex", 14, Color(0.75, 0.72, 0.65))
+	_add_label("Expected merges:", 14, Color(0.75, 0.72, 0.65))
+	_add_label("  [ENABLED]  rifle_range + barding_hall → war_academy", 13, Color(0.4, 0.9, 0.5))
+	_add_label(
+		"  [GATED]    rifle_range + powder_annex → gunnery_corps (needs military_synthesis)",
+		13,
+		Color(0.7, 0.5, 0.3),
+	)
+	_add_label("", 12, Color.WHITE)
+	_add_label("Merge panel populated below:", 13, Color(0.75, 0.72, 0.65))
+
+	_merge_panel = MergePanelScene.instantiate() as PanelContainer
+	_merge_panel.position = Vector2(24.0, 220.0)
+	_merge_panel.size = Vector2(600.0, 360.0)
+	add_child(_merge_panel)
+
+
+func _show_merge_panel() -> void:
+	var city: FakeCity = FakeCity.new()
+	var registry_json: String = "{}"
+	var techs: PackedStringArray = PackedStringArray()
+	_merge_panel.populate(city, registry_json, techs)
+
+
+func _add_label(text: String, font_size: int, color: Color) -> void:
+	var lbl: Label = Label.new()
+	lbl.text = text
+	lbl.add_theme_font_size_override("font_size", font_size)
+	lbl.add_theme_color_override("font_color", color)
+	_label_root.add_child(lbl)
+
+
+func _capture() -> void:
+	if _captured:
+		return
+	_captured = true
+	var dir: DirAccess = DirAccess.open("user://")
+	if dir != null and not dir.dir_exists("screenshots"):
+		dir.make_dir("screenshots")
+	var path: String = "user://screenshots/%s.png" % _screenshot_name
+	var img: Image = get_viewport().get_texture().get_image()
+	img.save_png(path)
+	var abs_path: String = ProjectSettings.globalize_path(path)
+	print("[proof] screenshot saved → ", abs_path)
+	get_tree().quit()

src/game/engine/scenes/tests/proof_hybrid_merge.tscn

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+[gd_scene load_steps=2 format=3 uid="uid://p1b59hybridmrg01"]
+
+[ext_resource type="Script" path="res://engine/scenes/tests/proof_hybrid_merge.gd" id="1"]
+
+[node name="ProofHybridMerge" type="Node"]
+script = ExtResource("1")