feat: add Lua 5.1 addon system with .toc loader and /run command

Foundation for WoW-compatible addon support:

- Vendor Lua 5.1.5 source as a static library (extern/lua-5.1.5)
- TocParser: parses .toc files (## directives + file lists)
- LuaEngine: Lua 5.1 VM with sandboxed stdlib (no io/os/debug),
  WoW-compatible print() that outputs to chat, GetTime() stub
- AddonManager: scans Data/interface/AddOns/ for .toc files,
  loads .lua files on world entry, skips LoadOnDemand addons
- /run <code> slash command for inline Lua execution
- HelloWorld test addon that prints to chat on load

Integration: AddonManager initialized after asset manager, addons
loaded once on first world entry, reset on logout. XML frame
parsing is deferred to a future step.

src/addons/addon_manager.cpp

@@ -0,0 +1,93 @@
+#include "addons/addon_manager.hpp"
+#include "core/logger.hpp"
+#include <algorithm>
+#include <filesystem>
+
+namespace fs = std::filesystem;
+
+namespace wowee::addons {
+
+AddonManager::AddonManager() = default;
+AddonManager::~AddonManager() { shutdown(); }
+
+bool AddonManager::initialize(game::GameHandler* gameHandler) {
+    if (!luaEngine_.initialize()) return false;
+    luaEngine_.setGameHandler(gameHandler);
+    return true;
+}
+
+void AddonManager::scanAddons(const std::string& addonsPath) {
+    addons_.clear();
+
+    std::error_code ec;
+    if (!fs::is_directory(addonsPath, ec)) {
+        LOG_INFO("AddonManager: no AddOns directory at ", addonsPath);
+        return;
+    }
+
+    std::vector<fs::path> dirs;
+    for (const auto& entry : fs::directory_iterator(addonsPath, ec)) {
+        if (entry.is_directory()) dirs.push_back(entry.path());
+    }
+    // Sort alphabetically for deterministic load order
+    std::sort(dirs.begin(), dirs.end());
+
+    for (const auto& dir : dirs) {
+        std::string dirName = dir.filename().string();
+        std::string tocPath = (dir / (dirName + ".toc")).string();
+        auto toc = parseTocFile(tocPath);
+        if (!toc) continue;
+
+        if (toc->isLoadOnDemand()) {
+            LOG_DEBUG("AddonManager: skipping LoadOnDemand addon: ", dirName);
+            continue;
+        }
+
+        LOG_INFO("AddonManager: registered addon '", toc->getTitle(),
+                 "' (", toc->files.size(), " files)");
+        addons_.push_back(std::move(*toc));
+    }
+
+    LOG_INFO("AddonManager: scanned ", addons_.size(), " addons");
+}
+
+void AddonManager::loadAllAddons() {
+    int loaded = 0, failed = 0;
+    for (const auto& addon : addons_) {
+        if (loadAddon(addon)) loaded++;
+        else failed++;
+    }
+    LOG_INFO("AddonManager: loaded ", loaded, " addons",
+             (failed > 0 ? (", " + std::to_string(failed) + " failed") : ""));
+}
+
+bool AddonManager::loadAddon(const TocFile& addon) {
+    bool success = true;
+    for (const auto& filename : addon.files) {
+        // For Step 1: only load .lua files, skip .xml (frame system not yet implemented)
+        std::string lower = filename;
+        for (char& c : lower) c = static_cast<char>(std::tolower(static_cast<unsigned char>(c)));
+
+        if (lower.size() >= 4 && lower.substr(lower.size() - 4) == ".lua") {
+            std::string fullPath = addon.basePath + "/" + filename;
+            if (!luaEngine_.executeFile(fullPath)) {
+                success = false;
+            }
+        } else if (lower.size() >= 4 && lower.substr(lower.size() - 4) == ".xml") {
+            LOG_DEBUG("AddonManager: skipping XML file '", filename,
+                      "' in addon '", addon.addonName, "' (XML frames not yet implemented)");
+        }
+    }
+    return success;
+}
+
+bool AddonManager::runScript(const std::string& code) {
+    return luaEngine_.executeString(code);
+}
+
+void AddonManager::shutdown() {
+    addons_.clear();
+    luaEngine_.shutdown();
+}
+
+} // namespace wowee::addons