feat(editor): add --gen-mesh-lantern hand-lantern primitive

81st procedural mesh primitive. Hand-held oil lantern via
4 stacked Y-axis cylinders:

  • base — short narrow disc (the foot the lantern sits on)
  • globe — wider taller cylinder (the glass enclosure
    holding the wick)
  • neck — narrow constriction above the globe (where the
    cap meets the body)
  • cap — wider short top (the metal hood that lets vent
    smoke escape)

Distinct from --gen-mesh-candle (just wax + saucer) and
--gen-mesh-urn (4-tier pottery shape) — lantern's
wide-narrow-wide tier sequence reads as a glass-enclosed
wick under a metal hood.

Useful for night-watch stations, ranger camps, dwarven
mine tunnels, mausoleum interiors, vigil scenes,
witch-hut shelves. Watertight under weld (verified 336
manifold edges, 0 boundary, 0 non-manifold).

tools/editor/cli_arg_required.cpp

@@ -61,6 +61,7 @@ const char* const kArgRequired[] = {
     "--gen-mesh-hitching-rail", "--gen-mesh-pillar-row",
     "--gen-mesh-statue-base", "--gen-mesh-bird-bath",
     "--gen-mesh-planter-box", "--gen-mesh-urn", "--gen-mesh-candle",
+    "--gen-mesh-lantern",
     "--gen-camp-pack", "--gen-blacksmith-pack", "--gen-village-pack",
     "--gen-temple-pack", "--gen-graveyard-pack",
     "--gen-garden-pack", "--gen-dock-pack", "--gen-tavern-pack",