Tighten cruise altitude and shallow out dives

- Cloud ceiling lowered from y=1.8 to y=1.5 (thinner deck)
- Cruise raised from y=2.0 to y=2.6 (clear margin above clouds)
- Dive endpoint raised from y=0.9 to y=1.2 (skims top, never deep)
- Dive exponent 5 -> 8 (much rarer dives)
- Early-out and ceiling bounds updated to match new y=1.5

vendor/clouds3d.js

@@ -92,8 +92,8 @@ var FRAG_SRC = [
     'float cloudDensity(vec3 p, float baseThresh) {',
         'float n = fbm3(p * 0.35 + vec3(0.0, 0.0, uTime * 0.06));',
         // Cloud layer thickness: between y=-0.3 (deck bottom)
-        // and y=1.8 (top), densest in the middle.
-        'float h = clamp((p.y + 0.3) / 2.1, 0.0, 1.0);',
+        // and y=1.5 (top), densest in the middle.
+        'float h = clamp((p.y + 0.3) / 1.8, 0.0, 1.0);',
         'float profile = 4.0 * h * (1.0 - h); // bell curve',
         'profile = max(profile, 0.0);',
         'return smoothstep(baseThresh, baseThresh + 0.18, n) * profile;',
@@ -118,9 +118,12 @@ var FRAG_SRC = [
         // cloud deck like an airliner cockpit. pow(...,n) shapes the
         // sin into short dips so we occasionally skim the cloud top.
         'float drift = uTime * uSpeed * 0.45;',
-        'float diveT = pow(0.5 + 0.5 * sin(uTime * 0.10), 5.0);',
-        // Cloud layer tops around y≈1.8. Cruise just above it.
-        'float camY = mix(2.0, 0.9, diveT);',
+        // pow(...,8) keeps dives rare: most of the time diveT≈0,
+        // and only spikes briefly to 1.
+        'float diveT = pow(0.5 + 0.5 * sin(uTime * 0.10), 8.0);',
+        // Cruise at y=2.6 (well above cloud ceiling y=1.5), dive to
+        // y=1.2 — close enough to skim the cloud top, never deep inside.
+        'float camY = mix(2.6, 1.2, diveT);',
         'vec3 ro = vec3(drift, camY, drift * 0.7);',
         // Ray direction: nearly level, like looking out a cockpit
         // window. Horizon sits around the middle of the frame.
@@ -135,13 +138,13 @@ var FRAG_SRC = [
         // 'stormy' -> low (overcast deck).
         'float baseThresh = mix(0.72, 0.40, uDensity);',
         // Skip the gap between camera and cloud top so we don't waste
-        // steps marching through clear sky. ray-Y = 2.0 = cloud ceiling.
-        'float t = (ro.y > 2.0 && rd.y < -0.001) ? (ro.y - 2.0) / -rd.y : 0.0;',
+        // steps marching through clear sky. ray-Y = 1.5 = cloud ceiling.
+        'float t = (ro.y > 1.5 && rd.y < -0.001) ? (ro.y - 1.5) / -rd.y : 0.0;',
         'float stepSize = 0.85;',
         'float trans = 1.0;',
         'for (int i = 0; i < 18; i++) {',
             'vec3 p = ro + rd * t;',
-            'if (p.y > 2.0 || p.y < -0.4) break;',
+            'if (p.y > 1.5 || p.y < -0.4) break;',
             'float d = cloudDensity(p, baseThresh);',
             'if (d > 0.005) {',
                 // Cloud shading: bottom = shadow, top = lit