fix(assets): review fixes — fog noise speed and kernel UV clamping

Deep fog noise scroll speed 0.045/0.03 → 0.06/0.045 to match D-059
15-20s breathing cycle spec. Clamp sample_visibility() UV coordinates
to [0,1] to prevent sticky gradient at map edges.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/shaders/fog.gdshader

@@ -44,7 +44,8 @@ float sample_visibility(vec2 uv) {
     for (float dy = -3.0; dy <= 3.0; dy += 1.0) {
         for (float dx = -3.0; dx <= 3.0; dx += 1.0) {
             float w = exp(-(dx * dx + dy * dy) / 8.0);
-            sum += texture(visibility_tex, uv + vec2(dx, dy) * t).r * w;
+            vec2 sample_uv = clamp(uv + vec2(dx, dy) * t, vec2(0.0), vec2(1.0));
+            sum += texture(visibility_tex, sample_uv).r * w;
             weight += w;
         }
     }
@@ -95,7 +96,7 @@ void fragment() {
             // Layer 3: Deep fog (previously explored, no longer in LOS)
             // D-059: near-monochrome, ~10% zone temperature tint, 15-20s breathing cycle
             vec3 zone_tint = texture(zone_tint_tex, tex_uv).rgb;
-            float noise_val = texture(noise_tex, tile * 0.015 + vec2(time * 0.045, time * 0.03)).r;
+            float noise_val = texture(noise_tex, tile * 0.015 + vec2(time * 0.06, time * 0.045)).r;
             vec3 tint_color = mix(vec3(0.04), zone_tint, 0.1);
             float alpha = mix(0.62, 0.76, noise_val);  // Fog breathes
             COLOR = vec4(tint_color, alpha);