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/ldebug.h

@@ -0,0 +1,33 @@
+/*
+** $Id: ldebug.h,v 2.3.1.1 2007/12/27 13:02:25 roberto Exp $
+** Auxiliary functions from Debug Interface module
+** See Copyright Notice in lua.h
+*/
+
+#ifndef ldebug_h
+#define ldebug_h
+
+
+#include "lstate.h"
+
+
+#define pcRel(pc, p)	(cast(int, (pc) - (p)->code) - 1)
+
+#define getline(f,pc)	(((f)->lineinfo) ? (f)->lineinfo[pc] : 0)
+
+#define resethookcount(L)	(L->hookcount = L->basehookcount)
+
+
+LUAI_FUNC void luaG_typeerror (lua_State *L, const TValue *o,
+                                             const char *opname);
+LUAI_FUNC void luaG_concaterror (lua_State *L, StkId p1, StkId p2);
+LUAI_FUNC void luaG_aritherror (lua_State *L, const TValue *p1,
+                                              const TValue *p2);
+LUAI_FUNC int luaG_ordererror (lua_State *L, const TValue *p1,
+                                             const TValue *p2);
+LUAI_FUNC void luaG_runerror (lua_State *L, const char *fmt, ...);
+LUAI_FUNC void luaG_errormsg (lua_State *L);
+LUAI_FUNC int luaG_checkcode (const Proto *pt);
+LUAI_FUNC int luaG_checkopenop (Instruction i);
+
+#endif