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

Ninth themed mesh pack after camp / blacksmith / village /
temple / graveyard / garden / dock / tavern. Mining-shaft
/ quarry-floor scene emitting a 7-primitive working-mine
layout:

  • gravel-pile — loose rubble from the dig
  • crate-stack — raw-ore cargo waiting for transport
  • mine-cart — underground transport
  • pillar-row — roof support pillars (the colonnade
    pattern reads as mine-shaft supports underground)
  • lantern — light source
  • workbench — assay / sorting station
  • hitching-post — mule / cart tie

Together these form a complete working-mine entrance /
quarry-floor layout. Uses 3 primitives newly added in
recent batches (mine-cart, pillar-row, lantern).

Composite-pack catalogue: camp + blacksmith + village +
temple + graveyard + garden + dock + tavern + mining =
9 themed mesh packs. --list-packs surfaces 14 total
including the pre-existing zone/project starters.

tools/editor/cli_arg_required.cpp

@@ -65,6 +65,7 @@ const char* const kArgRequired[] = {
     "--gen-camp-pack", "--gen-blacksmith-pack", "--gen-village-pack",
     "--gen-temple-pack", "--gen-graveyard-pack",
     "--gen-garden-pack", "--gen-dock-pack", "--gen-tavern-pack",
+    "--gen-mining-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",