Fix nuke fallout embers flickering forever ☢️

The ember/particle flicker in the fallout effect was gated only by the
fallout bit, which is permanent on tiles that stay unowned. It also ramped
to full strength as the per-tile heat decayed to 0 and animated on the
global tick, so it kept flickering indefinitely after the blast had cooled —
visible both as the bloom dots and (more prominently) as the ambient ember
light when dynamic lighting is enabled.

Fade both with heat so they vanish along with the glow:
- extract.frag.glsl: bloom dots multiplied by the glow's opacity
- fallout-light.frag.glsl: ember light multiplied by heat

Heat decay timing is unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/client/render/gl/shaders/day-night/fallout-light.frag.glsl

@@ -45,6 +45,10 @@ void main() {
     float flick = max(0.0, sin(uTick * tileRate + h1 * 12.0) * 0.8 + 0.2);
     flick *= flick;
     flick *= mix(uParticleFreshScale, 1.0, 1.0 - heat);
+    // Fade embers out with the heat. The fallout bit is permanent on tiles
+    // that stay unowned, so without this the ember light flickers forever
+    // once the blast has cooled.
+    flick *= heat;
     light += uEmberLightColor * flick * uEmberLightIntensity;
   }
 

src/client/render/gl/shaders/fallout-bloom/extract.frag.glsl

@@ -102,6 +102,10 @@ void main() {
     flick *= flick;
     // Dampen when fresh (high heat); ramp to full as heat decays.
     flick *= mix(uParticleFreshScale, 1.0, 1.0 - heat);
+    // Fade dots out with the glow. Heat decays to 0, but the fallout bit is
+    // permanent on tiles that stay unowned, so without this the dots flicker
+    // forever once the bloom is gone.
+    flick *= opacity;
     vec3 pc = mix(uParticleColorDark, uParticleColorBright, h1) * flick * uParticleStrength;
     float pa = max(pc.r, max(pc.g, pc.b));
     fragColor += vec4(pc, pa);