feat(editor): add --gen-mesh-chimney brick-stack primitive

60th procedural mesh primitive. Builds a chimney as two
axis-aligned boxes (uses the shared addFlatBox helper):

  • main shaft: rectangular brick stack of width × depth ×
    (height - capH)
  • protective cap: a slightly wider box on top (capExtra
    wider than shaft on every side) — the rain-throw crown
    that sits on real masonry chimneys

Set capH=0 for a bare unfinished stack. Default 0.45×0.45×
1.8 m shaft with a 0.10-tall cap reads at human scale for
rooftop placement.

Useful for cottage rooflines, blacksmith forges, alchemist
labs, dwarven longhouses — any structure with a fireplace
that needs visible vent. Watertight under weld (verified
via --info-mesh-stats: 36 manifold edges, 0 boundary, 0
non-manifold).

tools/editor/cli_help.cpp

@@ -228,6 +228,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Dock: flat plank deck on N pairs of square pilings (default 3.0/1.0/0.6/3/0.10/0.10)\n");
     std::printf("  --gen-mesh-pergola <wom-base> [length] [width] [height] [postR] [beamT] [crossbeams]\n");
     std::printf("                         Pergola: 4 corner posts + 2 perimeter beams + N cross beams (open lattice top, no panel)\n");
+    std::printf("  --gen-mesh-chimney <wom-base> [width] [depth] [height] [capH] [capExtra]\n");
+    std::printf("                         Chimney: rectangular brick shaft topped by a slightly wider rain-cap (default 0.45/0.45/1.8/0.10/0.05)\n");
     std::printf("  --gen-mesh-table <wom-base> [width] [depth] [height] [legThick] [topThick]\n");
     std::printf("                         Table: flat top slab on 4 corner legs (default 1.6/1.0/0.85/0.10/0.06)\n");
     std::printf("  --gen-mesh-lamppost <wom-base> [poleH] [poleT] [baseSize] [lanternSize] [lanternH]\n");