feat(editor): add --gen-mesh-beehive (skep) primitive

52nd procedural mesh: woven straw beehive (skep) — 4 stacked
tiers of decreasing width approximating a dome (100% / 90% /
70% / 40% of base width), an optional foundation plate
underneath, and a small entrance notch box on the +Z face
that reads as a cutout rather than texture detail.

Useful for druidic groves, beekeeper farms, hunter camps,
peasant cottages — anywhere a fantasy world wants honey
production. Defaults to 0.70m base × 0.85m tall with a
small 0.05m foundation plate.

tools/editor/main.cpp

@@ -157,6 +157,7 @@ int main(int argc, char* argv[]) {
         "--gen-mesh-ladder", "--gen-mesh-well", "--gen-mesh-signpost",
         "--gen-mesh-mailbox", "--gen-mesh-tombstone", "--gen-mesh-crate",
         "--gen-mesh-stool", "--gen-mesh-cauldron", "--gen-mesh-gate",
+        "--gen-mesh-beehive",
         "--gen-texture-gradient",
         "--gen-mesh-from-heightmap", "--export-mesh-heightmap",
         "--displace-mesh",