feat(editor): add --gen-texture-bamboo jungle-stalk pattern

62nd procedural texture: vertical bamboo stalks with
cylindrical sin² brightness shading + horizontal darker
node bands at regular Y intervals. Each stalk gets a small
hash-derived hue jitter (±15) so adjacent stalks don't
read as a perfect repeat.

Per-pixel logic:
  • 10% horizontal gap between stalks (gapFrac=0.10) →
    visible bg seam between bamboo stalks
  • Inside the stalk, brightness = sin²(insetFraction * π)
    rising from 0 at the stalk edge to 1 at the centerline
  • Every nodeY pixels, a `nodeBand`-tall horizontal strip
    has its brightness knocked down to 2/3 — the segmented
    bamboo joint look

Useful for jungle huts, pandaren / asian-themed architecture,
swamp boardwalks, tropical-tribe weapon trim, brewmaster
zone trim. Default 24-pitch / 64-spacing / 4-band reads as
adult-bamboo at typical 256x256 wall-tile scale.

tools/editor/cli_arg_required.cpp

@@ -94,7 +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",
+    "--gen-texture-mesh-screen", "--gen-texture-bamboo",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",