fix: make TestLevel load on 4.6.3; build geometry from GDScript

- test_level.tscn: minimal Node3D root (zero SubResource references)
- debug/test_level_builder.gd: runtime floor/walls/lighting/camera/UI
  shapes/meshes created from BoxShape3D/BoxMesh — no .tscn subresources
- project.godot: revert features to 4.6 (installed build is 4.6.3)

debug/test_level_builder.gd

@@ -0,0 +1,91 @@
+extends Node3D
+class_name TestLevelBuilder
+## Builds the test level ONLY from code — no .tscn SubResource references.
+## Attach to a Node3D and call build() from _ready().
+
+func build() -> void:
+	_build_floor()
+	_build_walls()
+	_build_lighting()
+	_build_camera()
+	_build_ui()
+
+
+func _box_static(pos: Vector3, size: Vector3, color: Color) -> StaticBody3D:
+	var body := StaticBody3D.new()
+	body.position = pos
+	body.name = "Static_" + str(pos)
+	add_child(body)
+	var shape := CollisionShape3D.new()
+	shape.shape = BoxShape3D.new()
+	shape.shape.size = size
+	body.add_child(shape)
+	var mesh := MeshInstance3D.new()
+	mesh.mesh = BoxMesh.new()
+	mesh.mesh.size = size
+	var mat := StandardMaterial3D.new()
+	mat.albedo_color = color
+	mesh.mesh.surface_set_material(0, mat)
+	body.add_child(mesh)
+	return body
+
+
+func _build_floor() -> void:
+	_box_static(Vector3(0, -1.1, 0), Vector3(30, 0.4, 30), Color(0.35, 0.25, 0.15))
+
+
+func _build_walls() -> void:
+	# Thin, tall walls for wallrun / walljump testing
+	_box_static(Vector3(0, 3, -15), Vector3(30, 6, 0.4), Color(0.55, 0.45, 0.35))
+	_box_static(Vector3(15, 3, 0),  Vector3(0.4, 6, 30), Color(0.55, 0.45, 0.35))
+	_box_static(Vector3(-15, 3, 0), Vector3(0.4, 6, 30), Color(0.55, 0.45, 0.35))
+
+
+func _build_lighting() -> void:
+	var sun := DirectionalLight3D.new()
+	sun.name = "Sun"
+	sun.position = Vector3(0, 10, 0)
+	sun.rotation_degrees = Vector3(50, 0, 0)
+	sun.light_color = Color(1, 0.95, 0.85)
+	sun.light_energy = 1.1
+	sun.shadow_enabled = true
+	add_child(sun)
+
+
+func _build_camera() -> void:
+	var cam := Camera3D.new()
+	cam.name = "FpsCamera"
+	cam.current = true
+	cam.position = Vector3(0, 1.7, 0)
+	cam.fov = 90.0
+	add_child(cam)
+	# Spawn marker
+	var spawn := Node3D.new()
+	spawn.name = "PlayerSpawn"
+	spawn.position = Vector3(0, 1.5, 8)
+	add_child(spawn)
+
+
+func _build_ui() -> void:
+	var canvas := CanvasLayer.new()
+	canvas.name = "UI"
+	add_child(canvas)
+	var speed := Label.new()
+	speed.name = "SpeedLabel"
+	speed.offset_left = 16
+	speed.offset_top = 16
+	speed.offset_right = 520
+	speed.offset_bottom = 48
+	speed.text = "Speed: 0.0 m/s | State: --- | Chain: +0%"
+	canvas.add_child(speed)
+	var help := Label.new()
+	help.name = "HelpLabel"
+	help.offset_left = 16
+	help.offset_top = 52
+	help.offset_right = 720
+	help.offset_bottom = 108
+	help.text = (
+		"WASD Move | Sprint=Shift | Slide=Ctrl+S | "
+		"Double-Jump=Space twice | Dash=LShift | Wall-Jump=Jump at wall"
+	)
+	canvas.add_child(help)