feat(editor): add --gen-mesh-well-pail wooden bucket primitive

86th procedural mesh primitive. Wooden well-pail / mop-
bucket:

  • body — closed cylindrical Y-axis cylinder via
    addClosedCylinderY (collision-watertight)
  • handle — thin horizontal box floating handleArc above
    the rim, spanning at least bodyR×2 wide so its ends
    align with the rim's outside edge

Without rotation the handle is a straight bar rather than
a true semicircle, but the bucket-with-handle silhouette
still reads correctly. handleArc parameter controls the
gap between rim and handle (small = handle touches rim;
larger = bucket-being-carried look).

Useful for well scenes (pairs with --gen-mesh-well),
servant-corridor mop scenes, kitchen prep stations,
homestead exteriors, dwarven mine shafts, ocean-ship
swabbing decks. Watertight under weld (verified 102
manifold edges, 0 boundary, 0 non-manifold).

tools/editor/cli_arg_required.cpp

@@ -70,7 +70,7 @@ const char* const kArgRequired[] = {
     "--gen-mesh-planter-box", "--gen-mesh-urn", "--gen-mesh-candle",
     "--gen-mesh-lantern", "--gen-mesh-chalice",
     "--gen-mesh-standing-torch", "--gen-mesh-scroll-case",
-    "--gen-mesh-stove",
+    "--gen-mesh-stove", "--gen-mesh-well-pail",
     "--gen-camp-pack", "--gen-blacksmith-pack", "--gen-village-pack",
     "--gen-temple-pack", "--gen-graveyard-pack",
     "--gen-garden-pack", "--gen-dock-pack", "--gen-tavern-pack",