feat(editor): add --gen-texture-damask 4-petal wallpaper motif

83rd procedural texture: ornate damask wallpaper pattern.
Per cell: 4-fold radial petal lobes formed by sin(theta*2)^2,
faded out toward the cell edge, plus a small filled center
dot to anchor the motif visually.

Reads as gilded fabric / palace wallpaper / noble-faction
tapestry — the missing classic-ornament category in the
catalogue (chevron / herringbone / argyle / houndstooth
cover modern geometric patterns; damask covers the older
Western-European decorative arts side).

Useful for: throne-room walls, cathedral interiors, royal
banners, tavern wallpaper, cushion textures, scroll backgrounds,
manuscript decoration, alchemy-shop bottle-label backdrops.

tools/editor/cli_arg_required.cpp

@@ -132,6 +132,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-scratched-metal", "--gen-texture-crackle",
     "--gen-texture-star", "--gen-texture-halftone",
     "--gen-texture-bayer", "--gen-texture-moon",
+    "--gen-texture-damask",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",