fix(render3d): the meadow is vegetation, and still water reads as water

Two changes that have been sitting uncommitted in this checkout, gathered as a recovery
point before the next run of work.

grass.vert: the blade existence gate tested green DOMINANCE - g - max(r, b) - which is a
test for lush green and nothing else. A dry alpine meadow is yellow-green, its red as high
as its green, so the meadow scored zero and was thinned to the floor - a QUARTER of the
blades - on exactly the ground that should be thickest. Measured on Maroon's own ortho,
g - max(r, b) reads +0.026 at the camp and -0.002 six hundred metres away, flipping between
full density and a quarter over continuous meadow; g - b reads +0.076 and +0.014 and
separates plant from rock and snow just as well, because rock and snow are neutral and
vegetation is not. Bare ground in the near band went 82% -> 57% looking down.

Blade height is biased short (h3 * h3) rather than spread evenly, so a meadow is a dense
mat with taller stems out of it; an even spread read as a lawn that had been cut.

water.frag: the planar reflection is returned at 0.72 of the scene's exposure rather than
all of it, the fresnel mix caps at 0.70 rather than 0.86, absorption falls so the bed is
visible through the surface at the angles a player stands at, and the ripple field is
roughly halved - so a sheltered lake is one sheet of water with a mountain in it instead
of open chop to the horizon.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/ludic.render3d/shaders/grass.vert

@@ -115,7 +115,15 @@ void main() {
   float ok = (1.0 - smoothstep(0.30, 0.55, 1.0 - gn.y)) * smoothstep(0.0, 0.6, ht.r - wl - 0.15) * smoothstep(u_snow_line - 80.0, u_snow_line - 200.0, ht.r);
   if (u_ortho_on > 0.5) {
     vec3 oc = textureLod(u_ortho, huv, 1.5).rgb;
-    ok *= 0.25 + 0.75 * smoothstep(0.0, 0.02, oc.g - max(oc.r, oc.b));
+    // Is this ground vegetated, by the photograph? The test used to be green DOMINANCE -
+    // g - max(r, b) - which is a test for lush green and nothing else. A dry alpine meadow
+    // is yellow-green: its red is as high as its green, so the whole meadow scored zero and
+    // was thinned to the floor, a quarter of the blades, on exactly the ground that should
+    // be thickest. Measured on Maroon's own ortho, g - max(r, b) reads +0.026 at the camp
+    // and -0.002 six hundred metres away, flipping between full density and a quarter over
+    // open meadow; g - b reads +0.076 and +0.014 and separates plant from rock and snow
+    // just as well, because rock and snow are neutral and vegetation is not.
+    ok *= 0.40 + 0.60 * smoothstep(0.0, 0.025, oc.g - oc.b);
   }
   if (h4 > ok) { cull(); return; }
   // the root on the drawn surface: the CDLOD mesh follows the B-spline to within
@@ -129,7 +137,13 @@ void main() {
   float ang = hv.y * 6.2831853;
   float s = sin(ang), c_ = cos(ang);
   float grow = spacing / u_s0;                       // 1 at the camera, growing with distance
-  float tall = mix(0.18, 0.42, h3) * mix(0.8, 1.2, hash1(cid * 0.1)) * (1.0 + 0.35 * smoothstep(1.0, 12.0, grow)) * life;
+  // Height is biased SHORT rather than spread evenly. A meadow is not one length of grass: it
+  // is a dense mat with taller stems and seed heads standing out of it, and h3 * h3 gives that
+  // for nothing - half the blades come out under a quarter of the range, and the few long ones
+  // are what carry the silhouette against the light. An even 0.18-0.42 spread read as a lawn
+  // that had been cut, which is the one thing an alpine meadow is not.
+  float hh = h3 * h3;
+  float tall = mix(0.09, 0.60, hh) * mix(0.8, 1.2, hash1(cid * 0.1)) * (1.0 + 0.35 * smoothstep(1.0, 12.0, grow)) * life;
   float bw = 0.028 * mix(1.0, 0.45 * grow, smoothstep(1.0, 4.0, grow));
   if (far) { bw = max(bw, spacing * 0.35); tall = min(tall, spacing * 0.3); }
   vec3 p = vec3(a_pos.x * bw, a_pos.y * tall, a_pos.z * tall * (0.6 + 0.8 * h4));