render3d: ground_fill_golden.json is valid JSON (the cover and solid blocks each closed one brace too many)

gg_cover_json and gg_solid_json ended in plain strings with "}}", which only a template literal reads as one
brace: the cover's closed the top-level object before "solid", and the solid's left a stray "}" at the end.
The committed golden is fixed by hand to what the generator now writes.

ground_fill_test also checks the golden as JSON: one value with nothing after it (Json.parse reads the
first value and ignores the rest, so it alone would not have caught this), an object, its eleven sections
in order. The generator notes what the studio asked: past the density patch an empty tile reads 0 for R and
G (only past the map's edge does a texel clamp), and several clearings multiply.

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

packages/ludic.render3d/tests/gen/ground_fill_golden.ludic

@@ -1,6 +1,12 @@
 # gen/ground_fill_golden.ludic - writes tests/ground_fill_golden.json from what ground_fill grows today. Run it
 # from the repository root after a deliberate change to the fill, and commit the file with the change.
 import "ludic.render3d/r3d.ludic"
+
+# Past the patch (tx0 .. tx0 + w - 1, all the chunk reads) an empty tile reads 0 for R and G, never its neighbour;
+# only a texel past the map's edge clamps to the edge texel (gd_texel, gd_fill), and a missing channel reads 128.
+
+# Several clearings MULTIPLY (ground_clear_at), in the order handed over: each floor..1, 1 past r_out, floor
+# clamped to 0..1, at most GD_CLEAR_MAX (32); a layer with trample multiplies its chance by the product.
 program GroundFillGolden {
   numbers float
   import "../fakes/ground_golden.ludic"