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/toc_parser.hpp

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <optional>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+namespace wowee::addons {
+
+struct TocFile {
+    std::string addonName;
+    std::string basePath;
+
+    std::unordered_map<std::string, std::string> directives;
+    std::vector<std::string> files;
+
+    std::string getTitle() const;
+    std::string getInterface() const;
+    bool isLoadOnDemand() const;
+};
+
+std::optional<TocFile> parseTocFile(const std::string& tocPath);
+
+} // namespace wowee::addons