feat(editor): add --gen-texture-carbon fiber-weave pattern

57th procedural texture: 2x2 cell pattern where alternating
cells hold horizontal vs vertical fiber segments. Each
segment gets a sin² brightness profile across its
perpendicular axis — 0 at the segment edge, peak at center —
giving the rounded highlight of a real woven fiber bundle.

Cell-pair parity (cx + cy) % 2 determines orientation, so
adjacent cells always alternate weave direction in both X
and Y. Reads as the unmistakable carbon-fiber checkerboard
even at small scales.

Useful for sci-fi armor, sleek tech panels, vehicle bodies,
ritual obsidian inlays, dwarven runeplate accents — any
"machined composite" surface where flat dark grey would
read as plain plastic.

Default 12-pixel cell at 256x256 reads cleanly with about
21 visible weave segments per side.

tools/editor/cli_arg_required.cpp

@@ -90,6 +90,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-rope", "--gen-texture-caustics",
     "--gen-texture-starburst", "--gen-texture-studs",
     "--gen-texture-moss", "--gen-texture-woodgrain",
+    "--gen-texture-carbon",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",