feat: full cel treatment for Neon Alley — flat toon colors + ink outlines

- LevelMaterials.flat(): toon-banded FLAT color material (no greybox grid
  texture) for dressed maps; cached per tint, rim/spec off
- Neon Alley overrides _box_static: every structure renders flat cel color;
  prop-scale pieces (<10m) get an inverted-hull ink outline scaled to their
  size. Building-scale boxes skip the hull — the inflated plates smear into
  black voids at close range (found via fixed street-camera capture)
- Pylon wires render as flat ink lines; warmer wood + hotter vermilion for
  flat shading (the grid multiply used to brighten tints)
- visual_capture: deterministic street-level shot after the aerial for
  style comparisons

Street capture now reads properly BoomerangX: flat lavender asphalt, hard
light bands, torii framed down the underpass, neon strips + sign glow.

Co-Authored-By: Claude Fable 5 <[email protected]>

debug/visual_capture.gd

@@ -48,6 +48,13 @@ func _process(_delta: float) -> bool:
 			aerial.current = true
 	elif _frames == 340:
 		_shot("aerial")
+		# Fixed street-level view for deterministic style comparisons
+		var cam := root.get_camera_3d()
+		if cam:
+			cam.global_position = Vector3(3, 2.2, 20)
+			cam.look_at(Vector3(-8, 4, -18), Vector3.UP)
+	elif _frames == 360:
+		_shot("street")
 		return true
 	return false