feat(editor): add --gen-mesh-firepit camp firepit primitive

54th procedural mesh primitive. Builds a recognizable
campfire setup from axis-aligned boxes only:

  • ring of N stone cubes evenly placed at radius ringR
    around the firepit center, sitting on the ground
  • two crossed log boxes at the center (one along X,
    one along Z, slightly raised) — the unmistakable
    visual cue separating a firepit from a generic
    decorative stone ring

Pairs naturally with --gen-mesh-tent for outdoor camp
set dressing (Horde encampments, Defias hideouts, scout
overlooks). Default 0.5-radius ring with 8 stones reads
cleanly at 1:1 player scale.

tools/editor/cli_arg_required.cpp

@@ -49,7 +49,7 @@ const char* const kArgRequired[] = {
     "--gen-mesh-banner", "--gen-mesh-grave", "--gen-mesh-bench",
     "--gen-mesh-shrine", "--gen-mesh-totem", "--gen-mesh-cage",
     "--gen-mesh-throne", "--gen-mesh-coffin", "--gen-mesh-bookshelf",
-    "--gen-mesh-tent",
+    "--gen-mesh-tent", "--gen-mesh-firepit",
     "--gen-mesh-table", "--gen-mesh-lamppost", "--gen-mesh-bed",
     "--gen-mesh-ladder", "--gen-mesh-well", "--gen-mesh-signpost",
     "--gen-mesh-mailbox", "--gen-mesh-tombstone", "--gen-mesh-crate",