atmosphere: cap haze alpha to avoid hard horizon cut

config.js

@@ -320,9 +320,10 @@ window.CONFIG = {
             enabled: true,
             heightKm: 60,
             scaleHeightKm: 8.5,
-            density: 0.25,
+            density: 0.18,
             grayTau: 1.2,
-            gain: 1.0
+            gain: 1.0,
+            maxAlpha: 0.55
         },
         model: {
             enabled: false        // legacy full atmosphere model remains off