clouds: restore cloud top to 12.9 km while keeping terrain occlusion disabled

config.js

@@ -144,7 +144,7 @@ window.CONFIG = {
     // altitude so aircraft fly above the deck.
     clouds: {
         enabled: true,
-        top: 1.55,                // ~20 km test deck
+        top: 1.0,                 // ~12.9 km
         bottom: -0.2,             // ~-2.6 km (deck base slightly below terrain)
         // Coverage per weather level, 0 = clear, 1 = overcast. Only the
         // levels listed here override the built-in defaults