feat(editor): BLP→PNG texture export for open format zones

- TextureExporter: converts Blizzard BLP textures to standard PNG
  for fully open redistribution of custom zones
- collectUsedTextures(): finds all texture paths referenced by terrain
- exportTexturesAsPng(): loads BLP via asset manager, writes RGBA PNG
  using stb_image_write to output/MapName/textures/
- Zone export now automatically converts all used textures to PNG
- Client's PNG override system already loads these automatically
  (checks for .png alongside .blp before loading)

Format replacement progress:
- DONE: ADT→WOT/WHM (terrain)
- DONE: WDT→zone.json (map definition)
- DONE: BLP→PNG (textures — auto-exported on zone save)
- TODO: DBC→JSON, M2→open model, WMO→open building

tools/editor/texture_exporter.cpp

@@ -0,0 +1,64 @@
+#include "texture_exporter.hpp"
+#include "pipeline/asset_manager.hpp"
+#include "pipeline/blp_loader.hpp"
+#include "core/logger.hpp"
+#include <filesystem>
+#include <algorithm>
+
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include "stb_image_write.h"
+
+namespace wowee {
+namespace editor {
+
+std::vector<std::string> TextureExporter::collectUsedTextures(const pipeline::ADTTerrain& terrain) {
+    std::unordered_set<std::string> unique;
+    for (const auto& tex : terrain.textures)
+        unique.insert(tex);
+    std::vector<std::string> result(unique.begin(), unique.end());
+    std::sort(result.begin(), result.end());
+    return result;
+}
+
+int TextureExporter::exportTexturesAsPng(pipeline::AssetManager* am,
+                                          const std::vector<std::string>& texturePaths,
+                                          const std::string& outputDir) {
+    namespace fs = std::filesystem;
+    int exported = 0;
+
+    for (const auto& texPath : texturePaths) {
+        auto blpImage = am->loadTexture(texPath);
+        if (!blpImage.isValid()) {
+            LOG_WARNING("Texture not found or invalid: ", texPath);
+            continue;
+        }
+
+        // Build output path: replace backslashes, change .blp to .png
+        std::string outPath = texPath;
+        std::replace(outPath.begin(), outPath.end(), '\\', '/');
+        // Lowercase
+        std::transform(outPath.begin(), outPath.end(), outPath.begin(),
+                       [](unsigned char c) { return std::tolower(c); });
+        // Change extension
+        auto dotPos = outPath.rfind('.');
+        if (dotPos != std::string::npos)
+            outPath = outPath.substr(0, dotPos) + ".png";
+
+        std::string fullPath = outputDir + "/" + outPath;
+        fs::create_directories(fs::path(fullPath).parent_path());
+
+        // Write RGBA data as PNG
+        if (stbi_write_png(fullPath.c_str(), blpImage.width, blpImage.height, 4,
+                           blpImage.data.data(), blpImage.width * 4)) {
+            exported++;
+        } else {
+            LOG_WARNING("Failed to write PNG: ", fullPath);
+        }
+    }
+
+    LOG_INFO("Exported ", exported, "/", texturePaths.size(), " textures as PNG to ", outputDir);
+    return exported;
+}
+
+} // namespace editor
+} // namespace wowee