feat: cel-shaded look — toon shader, ink outlines, stylized environment

- toon.gdshader: banded diffuse with cool-tinted shadows (3 tones), stepped
  specular, rim light, and an optional world-triplanar albedo path so level
  geometry keeps the 0.5 m grid with no UVs
- toon_outline.gdshader: inverted-hull ink outline, applied via
  material_overlay so it works on skinned (deforming) meshes
- LevelMaterials: tinted() now returns toon grid materials; toonify()/
  apply_toon_recursive() convert imported character/prop materials in place
- SkinnedPlayerModel: characters get toon shading + outline on load
- LevelEnvironment: shared stylized environment for all maps — saturated
  anime sky, linear tonemap (filmic/ACES crush cel bands), bloom for
  emissives, saturation+contrast grade, light depth haze; test level and
  dust2 now use it and the procedural arena (which had NO environment)
  gets it plus runtime toonification of its baked geometry

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

scenes/maps/level_environment.gd

@@ -0,0 +1,84 @@
+extends Object
+class_name LevelEnvironment
+
+## Shared stylized environment for every level: saturated anime-sky gradient,
+## bloom for emissives (tracers, plasma), and a color grade that pushes the
+## cel-shaded look (high saturation, slight contrast lift). Builders call
+## add_to(level) instead of hand-rolling WorldEnvironment + sun.
+
+
+## Creates and adds a WorldEnvironment + key sun + cool fill light.
+## Returns the WorldEnvironment node.
+static func add_to(level: Node, sky_variant: String = "day") -> WorldEnvironment:
+	var env := WorldEnvironment.new()
+	env.name = "WorldEnvironment"
+	env.environment = make_environment(sky_variant)
+	level.add_child(env)
+
+	if not level.has_node("Sun"):
+		var sun := DirectionalLight3D.new()
+		sun.name = "Sun"
+		sun.rotation_degrees = Vector3(-52, 38, 0)
+		sun.light_color = Color(1.0, 0.97, 0.88)
+		sun.light_energy = 1.4
+		sun.shadow_enabled = true
+		sun.directional_shadow_mode = DirectionalLight3D.SHADOW_PARALLEL_4_SPLITS
+		sun.directional_shadow_max_distance = 120.0
+		level.add_child(sun)
+
+		var fill := DirectionalLight3D.new()
+		fill.name = "FillLight"
+		fill.rotation_degrees = Vector3(-30, -142, 0)
+		fill.light_color = Color(0.6, 0.7, 1.0)
+		fill.light_energy = 0.25
+		fill.shadow_enabled = false
+		level.add_child(fill)
+	return env
+
+
+static func make_environment(sky_variant: String = "day") -> Environment:
+	var environment := Environment.new()
+	environment.background_mode = Environment.BG_SKY
+	var sky := Sky.new()
+	var sky_mat := ProceduralSkyMaterial.new()
+	match sky_variant:
+		"sunset":
+			sky_mat.sky_top_color = Color(0.25, 0.2, 0.5)
+			sky_mat.sky_horizon_color = Color(0.95, 0.6, 0.45)
+			sky_mat.ground_bottom_color = Color(0.18, 0.12, 0.2)
+			sky_mat.ground_horizon_color = Color(0.85, 0.55, 0.45)
+			sky_mat.sun_curve = 0.12
+		_:
+			# Bold anime day sky: deep saturated blue up top, bright cyan horizon.
+			sky_mat.sky_top_color = Color(0.18, 0.4, 0.85)
+			sky_mat.sky_horizon_color = Color(0.72, 0.88, 0.98)
+			sky_mat.ground_bottom_color = Color(0.22, 0.2, 0.24)
+			sky_mat.ground_horizon_color = Color(0.62, 0.7, 0.75)
+			sky_mat.sun_curve = 0.1
+	sky_mat.sun_angle_max = 20.0
+	sky.sky_material = sky_mat
+	environment.sky = sky
+
+	# Flat-ish ambient keeps toon shadow bands readable (sun does the shaping).
+	environment.ambient_light_source = Environment.AMBIENT_SOURCE_SKY
+	environment.ambient_light_energy = 0.55
+
+	# Filmic crushes the cel bands; linear-ish keeps them crisp.
+	environment.tonemap_mode = Environment.TONE_MAPPER_LINEAR
+
+	# Bloom sells emissives (tracers, plasma, rim highlights).
+	environment.glow_enabled = true
+	environment.glow_intensity = 0.5
+	environment.glow_bloom = 0.05
+	environment.glow_hdr_threshold = 1.1
+
+	# Cel color grade: punchy saturation, hint of contrast.
+	environment.adjustment_enabled = true
+	environment.adjustment_saturation = 1.22
+	environment.adjustment_contrast = 1.05
+
+	# A touch of depth haze for scale; far enough to not gray the arena.
+	environment.fog_enabled = true
+	environment.fog_light_color = Color(0.65, 0.75, 0.9)
+	environment.fog_density = 0.0012
+	return environment