feat(editor): add --gen-mesh-dock pier-on-stilts primitive

58th procedural mesh primitive. Builds a wooden waterside
dock from axis-aligned boxes:

  • flat plank deck slab spanning length × width at deckT
    thickness, sitting at deckHeight off the ground
  • N pairs of square pilings under the long edges, evenly
    spaced from end to end
  • pilings inset by pilingW so the deck overhangs slightly
    (the standard "boards rest ON TOP of the posts" look)

Distinct from --gen-mesh-bridge which arches OVER an
obstacle — a dock walks straight out from a shoreline on
stilts to the water. Useful for fishing villages, port
warehouses, lake settlements, ferry stations, smuggler
hideouts.

Watertight under weld (--audit-watertight passes): pilings
sit below the deck overhang and don't share corners with it.

tools/editor/cli_help.cpp

@@ -220,6 +220,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Canopy: 4-post awning with flat top panel and optional drape lips (default 1.6/1.2/2.0/0.05/0.03/0.15)\n");
     std::printf("  --gen-mesh-haystack <wom-base> [baseR] [height] [layers] [sides]\n");
     std::printf("                         Haystack: terraced stack of N frustums tapering to an apex point (default 0.6/0.9/3/12)\n");
+    std::printf("  --gen-mesh-dock <wom-base> [length] [width] [height] [pilings/side] [pilingW] [deckT]\n");
+    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-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");