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.

include/addons/addon_manager.hpp

@@ -0,0 +1,33 @@
+#pragma once
+
+#include "addons/lua_engine.hpp"
+#include "addons/toc_parser.hpp"
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace wowee::addons {
+
+class AddonManager {
+public:
+    AddonManager();
+    ~AddonManager();
+
+    bool initialize(game::GameHandler* gameHandler);
+    void scanAddons(const std::string& addonsPath);
+    void loadAllAddons();
+    bool runScript(const std::string& code);
+    void shutdown();
+
+    const std::vector<TocFile>& getAddons() const { return addons_; }
+    LuaEngine* getLuaEngine() { return &luaEngine_; }
+    bool isInitialized() const { return luaEngine_.isInitialized(); }
+
+private:
+    LuaEngine luaEngine_;
+    std::vector<TocFile> addons_;
+
+    bool loadAddon(const TocFile& addon);
+};
+
+} // namespace wowee::addons