refactor(editor): extract vertex weld into shared cli_weld utility

Three callers were each open-coding the same quantize-and-
bucket pass over vertex positions: --info-mesh-stats,
--info-wob-stats, and --bake-wom-collision. Move the
implementation to cli_weld.{hpp,cpp} as buildWeldMap() and
have each caller pass a flat positions array.

Identical std::map-based exact-equality keying preserved
(unbalanced-hash collisions remain absent). All three call
sites verified to produce byte-identical output:

  • info-mesh-stats firepit: 240→80 verts, 0 boundary
  • info-wob-stats cube:     8→8 verts, watertight YES
  • bake-wom-collision tent: 18→6 verts, 8-tri WOC

About 75 lines of duplication removed; future weld-using
commands now opt in by including one header.

tools/editor/cli_weld.cpp

@@ -0,0 +1,39 @@
+#include "cli_weld.hpp"
+
+#include <algorithm>
+#include <cmath>
+#include <map>
+#include <tuple>
+
+namespace wowee {
+namespace editor {
+namespace cli {
+
+std::vector<uint32_t> buildWeldMap(
+        const std::vector<glm::vec3>& positions,
+        float eps,
+        std::size_t& uniqueOut) {
+    const float invEps = 1.0f / std::max(eps, 1e-9f);
+    using QKey = std::tuple<int64_t, int64_t, int64_t>;
+    std::map<QKey, uint32_t> bucket;
+    std::vector<uint32_t> canon(positions.size());
+    for (std::size_t v = 0; v < positions.size(); ++v) {
+        const auto& p = positions[v];
+        QKey k{static_cast<int64_t>(std::lround(p.x * invEps)),
+               static_cast<int64_t>(std::lround(p.y * invEps)),
+               static_cast<int64_t>(std::lround(p.z * invEps))};
+        auto it = bucket.find(k);
+        if (it == bucket.end()) {
+            bucket.emplace(k, static_cast<uint32_t>(v));
+            canon[v] = static_cast<uint32_t>(v);
+        } else {
+            canon[v] = it->second;
+        }
+    }
+    uniqueOut = bucket.size();
+    return canon;
+}
+
+} // namespace cli
+} // namespace editor
+} // namespace wowee