feat(editor): add --gen-texture-plaid translucent-bands pattern

65th procedural texture: 2 sets of parallel "translucent"
bands — one horizontal, one vertical — overlaid on a base.
Each band contributes 0.5 alpha, so where bands cross both
half-alphas combine for the darkest color (the unmistakable
plaid grid intersection).

Distinct from --gen-texture-tartan (3-4 colors with
asymmetric stripe pitches) — this is the simple symmetric
2-color variant. Distinct from --gen-texture-checker (hard
binary squares) — plaid uses 3-tone alpha-blend gradient.

Useful for pub-table cloths, country-tavern napery, dwarven
formal-attire trim, picnic blankets, peasant-clothier
swatches. Default 24-stride / 8-band reads as classic
country-checked at 256x256.

First procedural texture to also use the new printPngWrote
helper from this batch.

tools/editor/cli_arg_required.cpp

@@ -99,6 +99,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-camo", "--gen-texture-snake-skin",
     "--gen-texture-mesh-screen", "--gen-texture-bamboo",
     "--gen-texture-blueprint", "--gen-texture-rust-streaks",
+    "--gen-texture-plaid",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",