feat: complete client integration for all 6 open formats

- Wire WOB buildings into WMO render pipeline (loads→converts→renders)
- Implement JSON DBC loading in DBCFile::loadJSON() with nlohmann/json
- Wire JSON DBC override into AssetManager (custom_zones/output scan)
- Add WMO→WOB conversion with full geometry (fromWMO)
- Replace placeholder WOB export with real WMO→WOB conversion in editor
- Add --convert-wmo CLI flag for batch WMO→WOB conversion
- Store discovered custom zones on Renderer with getCustomZones() accessor
- Add isCustomZone_ member to TerrainManager

All 6 Blizzard format replacements now fully load in the client:
  ADT→WOT/WHM, WDT→zone.json, BLP→PNG, DBC→JSON, M2→WOM, WMO→WOB

src/rendering/renderer.cpp

@@ -1887,13 +1887,11 @@ bool Renderer::initializeRenderers(pipeline::AssetManager* assetManager, const s
     LOG_INFO("Initializing renderers for map: ", mapName);
 
     // Scan for custom zones on first initialization
-    static bool customZonesScanned = false;
-    if (!customZonesScanned) {
-        customZonesScanned = true;
-        auto customZones = pipeline::CustomZoneDiscovery::scan({"custom_zones", "output"});
-        if (!customZones.empty()) {
+    if (customZones_.empty()) {
+        customZones_ = pipeline::CustomZoneDiscovery::scan({"custom_zones", "output"});
+        if (!customZones_.empty()) {
             LOG_INFO("=== Custom Zones Available ===");
-            for (const auto& z : customZones) {
+            for (const auto& z : customZones_) {
                 LOG_INFO("  ", z.name, " (", z.directory, ")",
                          z.hasCreatures ? " [NPCs]" : "",
                          z.hasQuests ? " [Quests]" : "");