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/all.c

@@ -0,0 +1,38 @@
+/*
+* all.c -- Lua core, libraries and interpreter in a single file
+*/
+
+#define luaall_c
+
+#include "lapi.c"
+#include "lcode.c"
+#include "ldebug.c"
+#include "ldo.c"
+#include "ldump.c"
+#include "lfunc.c"
+#include "lgc.c"
+#include "llex.c"
+#include "lmem.c"
+#include "lobject.c"
+#include "lopcodes.c"
+#include "lparser.c"
+#include "lstate.c"
+#include "lstring.c"
+#include "ltable.c"
+#include "ltm.c"
+#include "lundump.c"
+#include "lvm.c"
+#include "lzio.c"
+
+#include "lauxlib.c"
+#include "lbaselib.c"
+#include "ldblib.c"
+#include "liolib.c"
+#include "linit.c"
+#include "lmathlib.c"
+#include "loadlib.c"
+#include "loslib.c"
+#include "lstrlib.c"
+#include "ltablib.c"
+
+#include "lua.c"