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.

extern/lua-5.1.5/src/lualib.h

@@ -0,0 +1,53 @@
+/*
+** $Id: lualib.h,v 1.36.1.1 2007/12/27 13:02:25 roberto Exp $
+** Lua standard libraries
+** See Copyright Notice in lua.h
+*/
+
+
+#ifndef lualib_h
+#define lualib_h
+
+#include "lua.h"
+
+
+/* Key to file-handle type */
+#define LUA_FILEHANDLE		"FILE*"
+
+
+#define LUA_COLIBNAME	"coroutine"
+LUALIB_API int (luaopen_base) (lua_State *L);
+
+#define LUA_TABLIBNAME	"table"
+LUALIB_API int (luaopen_table) (lua_State *L);
+
+#define LUA_IOLIBNAME	"io"
+LUALIB_API int (luaopen_io) (lua_State *L);
+
+#define LUA_OSLIBNAME	"os"
+LUALIB_API int (luaopen_os) (lua_State *L);
+
+#define LUA_STRLIBNAME	"string"
+LUALIB_API int (luaopen_string) (lua_State *L);
+
+#define LUA_MATHLIBNAME	"math"
+LUALIB_API int (luaopen_math) (lua_State *L);
+
+#define LUA_DBLIBNAME	"debug"
+LUALIB_API int (luaopen_debug) (lua_State *L);
+
+#define LUA_LOADLIBNAME	"package"
+LUALIB_API int (luaopen_package) (lua_State *L);
+
+
+/* open all previous libraries */
+LUALIB_API void (luaL_openlibs) (lua_State *L); 
+
+
+
+#ifndef lua_assert
+#define lua_assert(x)	((void)0)
+#endif
+
+
+#endif