feat(editor): add --gen-texture-snake-skin diamond-scale pattern

60th procedural texture: brick-offset grid of diamond-shaped
scales using L1 (taxicab) metric so |dx|/halfW + |dy|/halfH
< 1 inside each diamond. Even rows are aligned with the cell
grid; odd rows shift by halfW so adjacent scales touch
tangentially along their points — the classic snake/dragon
hide pattern.

A thin dark outline at d ∈ [outlineFrac, 1] gives definition;
outline color is automatically derived as scaleHex × 0.4
(2/5 brightness). Set outlineW=0 to skip the outline for a
smoother painted-scale look.

Distinct from --gen-texture-scales (overlapping circles for
fish/dragon scales) and --gen-texture-chainmail (rings for
metal mail). Useful for snake-cult robe trim, naga skin,
dragon-scale armor inserts, lizardman set dressing,
basilisk-themed dungeon decor.

tools/editor/cli_help.cpp

@@ -153,6 +153,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Pinstripe: thin vertical lines at every stride; every Nth stripe is doubled-thick feature line\n");
     std::printf("  --gen-texture-camo <out.png> <aHex> <bHex> [cellSize] [threshold] [seed] [W H]\n");
     std::printf("                         Camouflage: 2-octave value noise thresholded into hard bg/fg blobs (woodland disruption pattern)\n");
+    std::printf("  --gen-texture-snake-skin <out.png> <bgHex> <scaleHex> [cellW] [cellH] [outlineW] [W H]\n");
+    std::printf("                         Snake skin: brick-offset diamond scales (L1 metric) with derived dark outline (reptile / dragon hide)\n");
     std::printf("  --add-texture-to-zone <zoneDir> <png-path> [renameTo]\n");
     std::printf("                         Copy an existing PNG into <zoneDir> (optionally renaming it on the way in)\n");
     std::printf("  --gen-mesh <wom-base> <cube|plane|sphere|cylinder|torus|cone|ramp> [size]\n");