render3d: the shadow array holds only the cascades a fog wall needs, and a thick fog takes the whole sky

A cascade that begins past the wall was fitted and cleared every frame for nothing: the array is now
made with the ones that begin inside it (2 at 30 m, 3 at 175 m, 5 without a fog) and made again when
the wall changes that count; shadow maps 80 -> 32 MB at 30 m, 48 MB at 175 m. A layer the array lacks
clamps to its last, read only past the wall where everything is fogged.

The sky: at walls of 110 m and nearer the whole sky is the fog's colour, overhead too, with a soft
glow at the sun or moon and no stars or clouds through it, easing out by 175 m; from 175 m on the
horizon band alone, and off as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.render3d/render.ludic

@@ -60,6 +60,7 @@ export function r3d_fog_wall(render3d_st: mut Render3dState, dist: float) -> voi
   render3d_st.sc_view_gen += 1
   cam_update(render3d_st)
   fog_impostors(render3d_st)
+  shadow_fog(render3d_st)
 }
 # how far anything is drawn: the fog wall and a margin, or `far` (0: no limit of its own) without one
 function r3d_reach(render3d_st: Render3dState, far: float) -> float {