render3d: the uniform ring is 16 MB a half and grows when a frame outgrows it; streamed layers are sized for the fog's reach

The ring held 2 x 64 MB of host memory for a frame that uses 3 MB at most (2761 draws at the
overlook, 1.7 MB in town): it starts at 16 MB a half, and a frame that ever runs out grows it for the
frames after (gvk_ring_grow, making the kept sets again; R3D_RING_KB=<n> starts small to watch it).
-95 MB at every fog level, off included.

A streamed layer's arrays and its stream's arena are made for the reach a fog wall leaves (twice its
area's share, at least 4096 instances) and emptied to refill within the frame budget
(fog_streams.ludic). The near streams' reach is already inside most walls, so it is -9 MB at 30 m.

R3D_VKMEM adds the ring's high-water mark, the largest buffers and the streamed layers' share.
Footprint at the overlook: 2008 MB off (2108 before this phase), 1748 MB at 175 m, 1682 MB at 30 m.

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

packages/ludic.render3d/render.ludic

@@ -61,6 +61,7 @@ export function r3d_fog_wall(render3d_st: mut Render3dState, dist: float) -> voi
   cam_update(render3d_st)
   fog_impostors(render3d_st)
   shadow_fog(render3d_st)
+  fog_streams(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 {