feat(editor): auto-export WMO buildings as WOB placeholders on zone save

- Zone export now creates WOB placeholder files for all placed WMO
  buildings in output/MapName/buildings/
- Full WMO→WOB conversion (with geometry) requires group file loading
  which is complex — placeholders reserve the path structure for now
- All 6 format conversions now auto-run on every zone export:
  ADT→WOT/WHM, BLP→PNG, DBC→JSON, M2→WOM, WMO→WOB, WDT→zone.json

tools/editor/editor_app.cpp

@@ -6,6 +6,7 @@
 #include "texture_exporter.hpp"
 #include "dbc_exporter.hpp"
 #include "pipeline/wowee_model.hpp"
+#include "pipeline/wowee_building.hpp"
 #include "core/coordinates.hpp"
 #include "rendering/vk_context.hpp"
 #include "pipeline/adt_loader.hpp"
@@ -755,6 +756,26 @@ void EditorApp::exportZone(const std::string& outputDir) {
             LOG_INFO("Converted ", convertedModels.size(), " M2 models to WOM");
     }
 
+    // Convert placed WMO buildings to WOB open format
+    if (objectPlacer_.objectCount() > 0) {
+        std::unordered_set<std::string> convertedWMOs;
+        for (const auto& obj : objectPlacer_.getObjects()) {
+            if (obj.type == PlaceableType::WMO && !convertedWMOs.count(obj.path)) {
+                // Create a placeholder WOB (full WMO→WOB conversion needs group loading)
+                pipeline::WoweeBuilding bld;
+                bld.name = obj.path;
+                std::string wobPath = obj.path;
+                std::replace(wobPath.begin(), wobPath.end(), '\\', '/');
+                auto dot = wobPath.rfind('.');
+                if (dot != std::string::npos) wobPath = wobPath.substr(0, dot);
+                pipeline::WoweeBuildingLoader::save(bld, base + "/buildings/" + wobPath);
+                convertedWMOs.insert(obj.path);
+            }
+        }
+        if (!convertedWMOs.empty())
+            LOG_INFO("Created ", convertedWMOs.size(), " WOB building placeholders");
+    }
+
     // Export used textures as PNG (open format replacement for BLP)
     auto usedTextures = TextureExporter::collectUsedTextures(terrain_);
     if (!usedTextures.empty()) {