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/etc/min.c

@@ -0,0 +1,39 @@
+/*
+* min.c -- a minimal Lua interpreter
+* loads stdin only with minimal error handling.
+* no interaction, and no standard library, only a "print" function.
+*/
+
+#include <stdio.h>
+
+#include "lua.h"
+#include "lauxlib.h"
+
+static int print(lua_State *L)
+{
+ int n=lua_gettop(L);
+ int i;
+ for (i=1; i<=n; i++)
+ {
+  if (i>1) printf("\t");
+  if (lua_isstring(L,i))
+   printf("%s",lua_tostring(L,i));
+  else if (lua_isnil(L,i))
+   printf("%s","nil");
+  else if (lua_isboolean(L,i))
+   printf("%s",lua_toboolean(L,i) ? "true" : "false");
+  else
+   printf("%s:%p",luaL_typename(L,i),lua_topointer(L,i));
+ }
+ printf("\n");
+ return 0;
+}
+
+int main(void)
+{
+ lua_State *L=lua_open();
+ lua_register(L,"print",print);
+ if (luaL_dofile(L,NULL)!=0) fprintf(stderr,"%s\n",lua_tostring(L,-1));
+ lua_close(L);
+ return 0;
+}