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/composition/vertical_slice/sunlit_shallows_world.tscn

@@ -0,0 +1,28 @@
+[gd_scene load_steps=5 format=3]
+
+[ext_resource type="PackedScene" path="res://game/world/sites/sunlit_shallows_environment.tscn" id="1_environment"]
+[ext_resource type="PackedScene" path="res://game/world/submarine/submarine_actor.tscn" id="2_submarine"]
+[ext_resource type="PackedScene" path="res://game/presentation/cockpit/cockpit_camera_rig.tscn" id="3_camera"]
+[ext_resource type="PackedScene" path="res://game/presentation/cockpit/cockpit_interior.tscn" id="4_cockpit"]
+
+[node name="SunlitShallowsWorld" type="Node3D"]
+
+[node name="Environment" parent="." instance=ExtResource("1_environment")]
+
+[node name="SubmarineActor" parent="." instance=ExtResource("2_submarine")]
+unique_name_in_owner = true
+position = Vector3(0, -30, 0)
+
+[node name="CockpitInterior" parent="SubmarineActor" instance=ExtResource("4_cockpit")]
+unique_name_in_owner = true
+
+[node name="CockpitCameraRig" parent="SubmarineActor" instance=ExtResource("3_camera")]
+unique_name_in_owner = true
+
+[node name="LeftProjector" parent="SubmarineActor" index="0"]
+light_energy = 3.0
+light_volumetric_fog_energy = 0.15
+
+[node name="RightProjector" parent="SubmarineActor" index="1"]
+light_energy = 3.0
+light_volumetric_fog_energy = 0.15