feat(editor): add --gen-texture-mesh-screen orthogonal grid

61st procedural texture: thin horizontal + vertical wires
forming an axis-aligned grid. Distinct from
--gen-texture-lattice (which uses ±45° diagonals to make
diamond openings) — this gives the right-angle window-
screen / chain-link / sci-fi-grille look.

Tested per-axis: a row is "on a wire" if (y % stride) <
wireW; a pixel falls on a wire if either its row OR its
column tests positive. Result is the unmistakable
orthogonal-mesh appearance.

Useful for window screens, anti-pest grates, fish nets,
sewer grilles, sci-fi vent panels, prison-cell windows,
goblin-workshop catwalks. Default 12-stride / 2-wide
gives a coarse mesh; finer versions read as bug screen.

tools/editor/cli_arg_required.cpp

@@ -94,6 +94,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-moss", "--gen-texture-woodgrain",
     "--gen-texture-carbon", "--gen-texture-pinstripe",
     "--gen-texture-camo", "--gen-texture-snake-skin",
+    "--gen-texture-mesh-screen",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",