feat(editor): --info-wob-stats + fix weld hash collision bug

Add --info-wob-stats reporting per-group + aggregate
triangle counts, surface area, edge analysis, and watertight
check for WOB buildings. Same flag surface as --info-mesh-stats
including --weld <eps> for true topological closure check
on per-face-vertex meshes.

Also fixes a correctness bug in the weld implementation
of --info-mesh-stats: the previous code used a 64-bit hash
of the quantized position as the equality key, which gave
false-positive collisions that incorrectly merged distinct
vertices. A unit cube's 8 corners collapsed to 2 positions
under the buggy hash. Replace with std::map keyed on the
actual quantized (qx, qy, qz) tuple so equality is exact.

Re-verified: cube 8→8 watertight YES; firepit 240→80
watertight YES (was wrongly reporting 56 unique with 48
non-manifold edges); tent_solid 18→6 watertight YES;
tent_fixed 21→9 with 5 boundary edges at the door perimeter
(correct — door is intentionally open).

tools/editor/cli_help.cpp

@@ -627,6 +627,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Aggregate WOM/WOB stats across an entire project (per-zone breakdown + totals)\n");
     std::printf("  --info-wob <wob-base> [--json]\n");
     std::printf("                         Print WOB building metadata (groups, portals, doodads) and exit\n");
+    std::printf("  --info-wob-stats <wob-base> [--weld <eps>] [--json]\n");
+    std::printf("                         Per-group + aggregate geometric stats (surface area, edges, watertight) for a WOB building\n");
     std::printf("  --info-woc <woc-path> [--json]\n");
     std::printf("                         Print WOC collision metadata (triangle counts, bounds) and exit\n");
     std::printf("  --info-wot <wot-base> [--json]\n");