feat(editor): add --gen-texture-pinstripe formal-fabric pattern

58th procedural texture: thin vertical lines at every
`stride` x position, with optional thicker "feature" line
every Nth stripe. The periodic doubled-thickness emphasis
is what distinguishes this from --gen-texture-stripes
(which renders wide alternating bands of each color).

Each stripe is centered within its column and has
configurable lineW; feature stripes are 2× the regular
width. Set featureEvery=0 to disable feature emphasis for
a uniform pinstripe pattern.

Useful for noble-house tabards, formal-attire fabric,
banker's counter cloth, sci-fi panel detailing, royal-
guard uniform trim, library / archive carpet runners.

Default 12-pixel stride, 1-pixel line, feature every 6th
stripe gives the classic suit-pinstripe look at 256x256.

tools/editor/cli_arg_required.cpp

@@ -90,7 +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",
+    "--gen-texture-carbon", "--gen-texture-pinstripe",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",