feat(editor): add --gen-graveyard-pack composite

Fifth themed mesh pack after camp / blacksmith / village /
temple. Cemetery scene emitting a 7-primitive burial yard:

  • grave — filled plot mound
  • tombstone — marker stone
  • coffin — above-ground or open
  • statue — mourning angel / patron deity
  • stone-bench — for visitors and mourners
  • gravel-pile — loose earth from a fresh dig
  • cage — fence section / mausoleum gate

Together these form the standard town-edge burial yard
when arranged in a zone. Composite-pack catalogue now:
camp + blacksmith + village + temple + graveyard.

All 7 outputs validate clean. --list-packs surfaces 10
composite flags total (5 mesh packs + the pre-existing
zone/project starter packs).

tools/editor/cli_arg_required.cpp

@@ -59,7 +59,7 @@ const char* const kArgRequired[] = {
     "--gen-mesh-archery-target", "--gen-mesh-gravel-pile",
     "--gen-mesh-stone-bench", "--gen-mesh-mine-cart",
     "--gen-camp-pack", "--gen-blacksmith-pack", "--gen-village-pack",
-    "--gen-temple-pack",
+    "--gen-temple-pack", "--gen-graveyard-pack",
     "--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",