Add hex-diamond island terrain prototype

New standalone debug prototype exploring the "gem-cut" flying island
shape: a flat hexagonal table (center region) surrounded by 6 sloped
trapezoidal facets down to the girdle (6 outer regions), with a
non-walkable 6-sided pavilion pyramid below for the underside. Crown
gets trimesh collision for later player testing; all 6 outer facets
stay visually neutral (alternating flat color only) since theming
comes later. Doesn't touch main.tscn or the old cross-layout prototype.

debug/HexDiamondIsland.gd

@@ -0,0 +1,105 @@
+extends Node3D
+
+# ═══════════════════════════════════════════════════════════════
+# HEX-DIAMANT-INSEL — Blockout
+# Krone (begehbar): flaches 6-Eck-Tisch + 6 Trapez-Facetten zur Rundiste
+# Pavillon (rein optisch): steile 6-seitige Pyramide unter der Rundiste
+# ═══════════════════════════════════════════════════════════════
+
+@export var table_radius    : float = 80.0    # flaches Sechseck in der Mitte
+@export var girdle_radius   : float = 260.0   # äußerer Sechseck-Rand (Rundiste)
+@export var crown_drop      : float = 30.0    # Höhenabfall Tisch -> Rundiste
+@export var pavilion_depth  : float = 190.0   # Höhenabfall Rundiste -> Spitze
+@export var angle_offset_deg: float = 0.0
+
+const COLOR_TABLE    := Color(0.75, 0.74, 0.70)
+const COLOR_FACET_A  := Color(0.55, 0.55, 0.48)
+const COLOR_FACET_B  := Color(0.49, 0.49, 0.43)
+const COLOR_PAVILION := Color(0.30, 0.28, 0.26)
+
+func _ready() -> void:
+	_build_crown()
+	_build_pavilion()
+
+func _hex_angle(k: int) -> float:
+	return deg_to_rad(angle_offset_deg) + float(k) / 6.0 * TAU
+
+func _add_tri(st: SurfaceTool, a: Vector3, b: Vector3, c: Vector3, col: Color) -> void:
+	var n := (b - a).cross(c - a).normalized()
+	for v in [a, b, c]:
+		st.set_normal(n)
+		st.set_color(col)
+		st.add_vertex(v)
+
+# ═══════════════════════════════════════════════
+# KRONE — Tisch + 6 Facetten (begehbar, mit Kollision)
+# ═══════════════════════════════════════════════
+func _build_crown() -> void:
+	var st := SurfaceTool.new()
+	st.begin(Mesh.PRIMITIVE_TRIANGLES)
+
+	var center := Vector3.ZERO
+	var table_pts  : Array[Vector3] = []
+	var girdle_pts : Array[Vector3] = []
+	for k in range(6):
+		var a := _hex_angle(k)
+		table_pts.append(Vector3(cos(a) * table_radius, 0.0, sin(a) * table_radius))
+		girdle_pts.append(Vector3(cos(a) * girdle_radius, -crown_drop, sin(a) * girdle_radius))
+
+	# Tisch-Fan (Zentrum-Region)
+	for k in range(6):
+		var k1 := (k + 1) % 6
+		_add_tri(st, center, table_pts[k1], table_pts[k], COLOR_TABLE)
+
+	# 6 Facetten (Außenregionen), abwechselnd eingefärbt für sichtbare Nähte
+	for k in range(6):
+		var k1 := (k + 1) % 6
+		var col := COLOR_FACET_A if k % 2 == 0 else COLOR_FACET_B
+		_add_tri(st, table_pts[k],  table_pts[k1],  girdle_pts[k], col)
+		_add_tri(st, table_pts[k1], girdle_pts[k1], girdle_pts[k], col)
+
+	var mesh := st.commit()
+	var mat := StandardMaterial3D.new()
+	mat.vertex_color_use_as_albedo = true
+	mat.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
+	mat.cull_mode = BaseMaterial3D.CULL_DISABLED
+	mesh.surface_set_material(0, mat)
+
+	var body := StaticBody3D.new()
+	body.name = "Crown"
+	var mi := MeshInstance3D.new()
+	mi.mesh = mesh
+	body.add_child(mi)
+	var cs := CollisionShape3D.new()
+	cs.shape = mesh.create_trimesh_shape()
+	body.add_child(cs)
+	add_child(body)
+
+# ═══════════════════════════════════════════════
+# PAVILLON — Pyramide unter der Rundiste (rein optisch)
+# ═══════════════════════════════════════════════
+func _build_pavilion() -> void:
+	var st := SurfaceTool.new()
+	st.begin(Mesh.PRIMITIVE_TRIANGLES)
+
+	var apex := Vector3(0, -crown_drop - pavilion_depth, 0)
+	var girdle_pts: Array[Vector3] = []
+	for k in range(6):
+		var a := _hex_angle(k)
+		girdle_pts.append(Vector3(cos(a) * girdle_radius, -crown_drop, sin(a) * girdle_radius))
+
+	for k in range(6):
+		var k1 := (k + 1) % 6
+		_add_tri(st, girdle_pts[k], girdle_pts[k1], apex, COLOR_PAVILION)
+
+	var mesh := st.commit()
+	var mat := StandardMaterial3D.new()
+	mat.vertex_color_use_as_albedo = true
+	mat.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
+	mat.cull_mode = BaseMaterial3D.CULL_DISABLED
+	mesh.surface_set_material(0, mat)
+
+	var mi := MeshInstance3D.new()
+	mi.name = "Pavilion"
+	mi.mesh = mesh
+	add_child(mi)

debug/hex_diamond_island.tscn

@@ -0,0 +1,32 @@
+[gd_scene format=3]
+
+[ext_resource type="Script" uid="uid://bia8axed2ndwj" path="res://debug/FreeCam.gd" id="1_freecam"]
+[ext_resource type="Script" path="res://debug/HexDiamondIsland.gd" id="2_hexdi"]
+
+[sub_resource type="Environment" id="Environment_hexdi"]
+background_mode = 1
+background_color = Color(0.16470589, 0.25490198, 0.36078432, 1)
+ambient_light_source = 2
+ambient_light_color = Color(0.23529412, 0.25490198, 0.29411766, 1)
+ambient_light_energy = 0.8
+
+[node name="HexDiamondIsland" type="Node3D"]
+
+[node name="WorldEnvironment" type="WorldEnvironment" parent="."]
+environment = SubResource("Environment_hexdi")
+
+[node name="Sun" type="DirectionalLight3D" parent="."]
+transform = Transform3D(0.8660254, -0.35355338, 0.35355338, 0, 0.70710677, 0.70710677, -0.5, -0.6123724, 0.6123724, 0, 0, 0)
+light_energy = 1.2
+
+[node name="FlyCamera" type="Node3D" parent="."]
+transform = Transform3D(1, 0, 0, 0, 0.92718387, 0.3746066, 0, -0.3746066, 0.92718387, 0, 120, 350)
+script = ExtResource("1_freecam")
+
+[node name="Camera3D" type="Camera3D" parent="FlyCamera"]
+fov = 65.0
+near = 0.1
+far = 1000.0
+
+[node name="HexDiamondIsland" type="Node3D" parent="."]
+script = ExtResource("2_hexdi")