feat(editor): add --gen-mesh-hitching-post stable fixture

67th procedural mesh primitive. Standard town/stable
hitching post:

  • two vertical posts separated by `span`
  • horizontal cross-bar at upper-post height (length =
    span - postW so it tucks INSIDE the post inner faces,
    matching real fence joinery)
  • optional decorative caps on each post — set capH=0
    for a bare working-yard post

All axis-aligned boxes, exercises every shared helper
(stripExt, initWomDefaults, addFlatBox,
finalizeAsSingleBatch, saveWomOrError). Watertight under
weld (verified 90 manifold edges, 0 boundary, 0
non-manifold).

Useful for stables, taverns with mount parking, town
squares, frontier outposts, ranger camps, post-and-rail
fence segments.

tools/editor/cli_arg_required.cpp

@@ -54,7 +54,7 @@ const char* const kArgRequired[] = {
     "--gen-mesh-pergola", "--gen-mesh-chimney", "--gen-mesh-bedroll",
     "--gen-mesh-workbench", "--gen-mesh-crate-stack",
     "--gen-mesh-watchpost", "--gen-mesh-water-trough",
-    "--gen-mesh-training-dummy",
+    "--gen-mesh-training-dummy", "--gen-mesh-hitching-post",
     "--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",