feat(editor): add --gen-texture-gear-cog mechanical wheel

85th procedural texture: gear-cog wheel pattern tiled per
cell. Three concentric radii define the gear:
  • hub   (rNorm < 0.20) — center axle hole, kept as bg
  • inner (rNorm < 0.65) — gap floor between teeth
  • outer (rNorm < 0.92) — tooth tip

Teeth alternate around the gear via a per-tooth phase
calculation: theta is mapped into a tooth period of
2*pi/teeth, with the first half of each period rendering
as a tooth (effective radius = outer) and the second half
rendering as a gap (effective radius = inner).

Useful for: engineering crafting backdrops, mechanical
door textures, gnomish / goblin themed gear icons,
factory / forge tile sets, clockwork-themed dungeons,
steampunk faction insignia, machinery damage states.

Distinct from --gen-texture-rings (concentric circles only,
no teeth). The first procedural texture in the catalogue
that exercises a per-tooth periodic offset rather than a
fixed angular fold.

tools/editor/cli_arg_required.cpp

@@ -198,6 +198,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-star", "--gen-texture-halftone",
     "--gen-texture-bayer", "--gen-texture-moon",
     "--gen-texture-damask", "--gen-texture-snowflake",
+    "--gen-texture-gear-cog",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",