Replace MPQ runtime with loose file asset system

Extract assets from MPQ archives into organized loose files indexed by
manifest.json, enabling fully parallel reads without StormLib serialization.
Add asset_extract and blp_convert tools, PNG texture override support.

src/pipeline/asset_manifest.cpp

@@ -0,0 +1,97 @@
+#include "pipeline/asset_manifest.hpp"
+#include "core/logger.hpp"
+#include <nlohmann/json.hpp>
+#include <fstream>
+#include <filesystem>
+#include <chrono>
+
+namespace wowee {
+namespace pipeline {
+
+bool AssetManifest::load(const std::string& manifestPath) {
+    auto startTime = std::chrono::steady_clock::now();
+
+    std::ifstream file(manifestPath);
+    if (!file.is_open()) {
+        LOG_ERROR("Failed to open manifest: ", manifestPath);
+        return false;
+    }
+
+    nlohmann::json doc;
+    try {
+        doc = nlohmann::json::parse(file);
+    } catch (const nlohmann::json::parse_error& e) {
+        LOG_ERROR("Failed to parse manifest JSON: ", e.what());
+        return false;
+    }
+
+    // Read header
+    int version = doc.value("version", 0);
+    if (version != 1) {
+        LOG_ERROR("Unsupported manifest version: ", version);
+        return false;
+    }
+
+    basePath_ = doc.value("basePath", "assets");
+    manifestDir_ = std::filesystem::path(manifestPath).parent_path().string();
+
+    // If basePath is relative, resolve against manifest directory
+    if (!basePath_.empty() && basePath_[0] != '/') {
+        basePath_ = manifestDir_ + "/" + basePath_;
+    }
+
+    // Parse entries
+    auto& entriesObj = doc["entries"];
+    if (!entriesObj.is_object()) {
+        LOG_ERROR("Manifest missing 'entries' object");
+        return false;
+    }
+
+    entries_.reserve(entriesObj.size());
+    for (auto& [key, val] : entriesObj.items()) {
+        Entry entry;
+        entry.filesystemPath = val.value("p", "");
+        entry.size = val.value("s", uint64_t(0));
+
+        // Parse CRC32 from hex string
+        std::string hexHash = val.value("h", "");
+        if (!hexHash.empty()) {
+            entry.crc32 = static_cast<uint32_t>(std::strtoul(hexHash.c_str(), nullptr, 16));
+        } else {
+            entry.crc32 = 0;
+        }
+
+        entries_[key] = std::move(entry);
+    }
+
+    loaded_ = true;
+
+    auto elapsed = std::chrono::steady_clock::now() - startTime;
+    auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(elapsed).count();
+    LOG_INFO("Loaded asset manifest: ", entries_.size(), " entries in ", ms, "ms (base: ", basePath_, ")");
+
+    return true;
+}
+
+const AssetManifest::Entry* AssetManifest::lookup(const std::string& normalizedWowPath) const {
+    auto it = entries_.find(normalizedWowPath);
+    if (it != entries_.end()) {
+        return &it->second;
+    }
+    return nullptr;
+}
+
+std::string AssetManifest::resolveFilesystemPath(const std::string& normalizedWowPath) const {
+    auto it = entries_.find(normalizedWowPath);
+    if (it == entries_.end()) {
+        return {};
+    }
+    return basePath_ + "/" + it->second.filesystemPath;
+}
+
+bool AssetManifest::hasEntry(const std::string& normalizedWowPath) const {
+    return entries_.find(normalizedWowPath) != entries_.end();
+}
+
+} // namespace pipeline
+} // namespace wowee