Add sunlit shallows site with localized sun shafts

New visual test site under game/world/sites: flat sandy floor at
-40 m, calm surface at 0 m, fixed daytime sun ahead of and above
the submarine. Light shafts come from a shadow-only surface
occluder whose alpha-scissor ripples open only inside a pool a few
tens of metres ahead; a subtractive FogVolume cancels the global
volumetric fog above the water, and an unshaded ceiling mesh shows
the lit underside of the surface inside that pool. A composed
world (sunlit_shallows_world.tscn) mounts the submarine, cockpit
and camera rig in it, with the projectors kept out of the fog.

Cockpit: the porthole glass moves to its own render layer with a
rougher material and the porthole fill light excludes that layer,
so interior lamps no longer mirror as hard specular points.

Quality gate: new integration suite for the site (42 checks), three
glass assertions in the foundation suite, and the Input-access
architecture rule now matches both path separators so the gate runs
on Windows. project.godot raises the volumetric fog froxel grid to
128 so the shafts stay readable.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

game/world/sites/sunlit_shallows_environment.tscn

@@ -0,0 +1,64 @@
+[gd_scene load_steps=3 format=3]
+
+[ext_resource type="Script" path="res://game/world/sites/sunlit_shallows_environment.gd" id="1_environment"]
+
+[sub_resource type="Environment" id="EnvironmentSunlitShallows"]
+background_mode = 1
+background_color = Color(0.005, 0.03, 0.06, 1)
+ambient_light_source = 3
+ambient_light_color = Color(0.14, 0.32, 0.42, 1)
+ambient_light_energy = 0.22
+tonemap_mode = 2
+tonemap_exposure = 0.75
+glow_enabled = true
+glow_levels/1 = 0.6
+glow_levels/2 = 1.0
+glow_levels/3 = 0.8
+glow_levels/4 = 0.3
+glow_intensity = 0.35
+glow_blend_mode = 0
+glow_hdr_threshold = 1.6
+fog_enabled = true
+fog_light_color = Color(0.04, 0.16, 0.24, 1)
+fog_light_energy = 0.12
+fog_sun_scatter = 0.0
+fog_density = 0.003
+fog_aerial_perspective = 0.6
+fog_sky_affect = 1.0
+volumetric_fog_enabled = true
+volumetric_fog_density = 0.035
+volumetric_fog_albedo = Color(0.26, 0.52, 0.7, 1)
+volumetric_fog_emission_energy = 0.0
+volumetric_fog_anisotropy = 0.55
+volumetric_fog_length = 150.0
+volumetric_fog_detail_spread = 1.6
+volumetric_fog_ambient_inject = 0.015
+volumetric_fog_sky_affect = 1.0
+volumetric_fog_temporal_reprojection_enabled = true
+volumetric_fog_temporal_reprojection_amount = 0.92
+
+[node name="SunlitShallowsEnvironment" type="Node3D"]
+script = ExtResource("1_environment")
+
+[node name="WorldEnvironment" type="WorldEnvironment" parent="."]
+environment = SubResource("EnvironmentSunlitShallows")
+
+[node name="Sun" type="DirectionalLight3D" parent="."]
+rotation_degrees = Vector3(-44, 162, 0)
+light_color = Color(0.86, 0.95, 1, 1)
+light_energy = 1.0
+light_volumetric_fog_energy = 1.4
+shadow_enabled = true
+shadow_bias = 0.04
+shadow_normal_bias = 1.5
+shadow_blur = 2.5
+directional_shadow_mode = 1
+directional_shadow_split_1 = 0.2
+directional_shadow_blend_splits = true
+directional_shadow_max_distance = 160.0
+
+[node name="ObserverCamera" type="Camera3D" parent="."]
+transform = Transform3D(1, 0, 0, 0, 0.9962, 0.0872, 0, -0.0872, 0.9962, 0, -30, 0)
+fov = 72.0
+near = 0.1
+far = 400.0