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_surface_occluder.gdshader

@@ -0,0 +1,39 @@
+// Calm-water surface seen only through its shadow: the mesh is invisible
+// (SHADOW_ONLY) and the alpha-scissor cut-outs let the fixed daytime sun carve
+// light shafts into the volumetric fog below.
+shader_type spatial;
+render_mode cull_disabled, unshaded, depth_prepass_alpha;
+
+uniform sampler2D ripple_noise : repeat_enable, filter_linear_mipmap;
+uniform float ripple_scale = 0.025;
+uniform float drift_speed = 0.012;
+uniform float coverage : hint_range(0.0, 1.0) = 0.30;
+// World-space pool where the surface lets sunlight through. Outside it the
+// surface is fully opaque, so shafts only form in that patch of water.
+uniform vec2 pool_center_xz = vec2(-14.0, -31.0);
+uniform float pool_radius = 22.0;
+uniform float pool_edge = 12.0;
+
+varying vec2 world_xz;
+
+void vertex() {
+	world_xz = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xz;
+}
+
+void fragment() {
+	vec2 slow_drift = TIME * drift_speed * vec2(1.0, 0.35);
+	vec2 cross_drift = TIME * drift_speed * vec2(-0.4, 0.9);
+	float broad = texture(ripple_noise, world_xz * ripple_scale + slow_drift).r;
+	float fine = texture(ripple_noise, world_xz * ripple_scale * 1.9 + cross_drift).r;
+	float raw_ripple = broad * 0.65 + fine * 0.35;
+	// Inside the pool the crests are sharpened so the gaps cut crisp shafts.
+	float pool_ripple = smoothstep(0.35, 0.65, raw_ripple);
+	// Outside the pool only the deepest troughs open: a dim dapple, not darkness.
+	float dim_ripple = smoothstep(0.16, 0.30, raw_ripple);
+	float pool = 1.0 - smoothstep(
+		pool_radius - pool_edge, pool_radius, distance(world_xz, pool_center_xz)
+	);
+	ALBEDO = vec3(0.0);
+	ALPHA = mix(dim_ripple, pool_ripple, pool);
+	ALPHA_SCISSOR_THRESHOLD = coverage;
+}