feat(editor): add --gen-mesh-mug tankard primitive

87th procedural mesh: drinking mug / tankard built from a
closed cylindrical body plus a thin side handle slab. The
handle is positioned on +X with its inner face flush against
the body and centered vertically.

Without rotation the handle is a solid box rather than a
real C-loop, so silhouette reads as a tankard handle rather
than a delicate ring — appropriate for the chunky-prop
aesthetic favored by the existing primitive set. Distinct
from --gen-mesh-chalice (3-tier goblet, no handle) and
--gen-mesh-well-pail (top horizontal handle bar).

Useful for tavern / banquet hall / kitchen dressing, inn
table props, and the eventual --gen-tavern-pack-2 follow-on
(once enough drinking-vessel primitives exist to justify a
dedicated drinkware composite).

86 verts / 68 tris at default 14 sides — a single batch
with shared body + handle texture coords.

tools/editor/cli_help.cpp

@@ -338,6 +338,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Pot-bellied stove: round cylindrical body + thin chimney column on top (cottage / workshop heating)\n");
     std::printf("  --gen-mesh-well-pail <wom-base> [bodyR] [bodyH] [handleW] [handleT] [handleArc] [sides]\n");
     std::printf("                         Wooden well-pail: closed cylindrical body + thin horizontal handle bar above (water-haul / mop-bucket prop)\n");
+    std::printf("  --gen-mesh-mug <wom-base> [bodyR] [bodyH] [handleW] [handleH] [handleArm] [sides]\n");
+    std::printf("                         Drinking mug / tankard: closed cylinder body + side handle slab (tavern / banquet / inn dressing)\n");
     std::printf("  --gen-camp-pack <outDir>\n");
     std::printf("                         Convenience: emit tent + firepit + bedroll + canopy + woodpile + haystack into outDir as 6 .wom files\n");
     std::printf("  --gen-blacksmith-pack <outDir>\n");