feat(editor): add --gen-texture-planks floor-board pattern

49th procedural texture: horizontal plank-floor pattern.
Each plank gets:

  • a hash-derived per-plank brightness offset (-24..+24)
    so adjacent boards read as separate pieces of wood
    rather than one long stripe
  • a 1px horizontal seam at its bottom edge
  • a 1px vertical end-seam at a hash-jittered x position,
    staggering plank ends across rows
  • optional darker grain streaks at evenly-spaced columns
    (jittered per plank so the pattern doesn't grid-align)

Useful for inn/tavern floors, ship deck planking, bridge
surfaces, market-stall counters, and any wood-floor surface
where the existing single-grain --gen-texture-wood would
read as one giant board.

Default 16px plank height with 5 grain streaks gives a
recognizable floor at 256x256 without aliasing.

tools/editor/cli_arg_required.cpp

@@ -83,6 +83,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-cracked", "--gen-texture-runes",
     "--gen-texture-leopard", "--gen-texture-zebra",
     "--gen-texture-knit", "--gen-texture-chainmail",
+    "--gen-texture-planks",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",