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/test/globals.lua

@@ -0,0 +1,13 @@
+-- reads luac listings and reports global variable usage
+-- lines where a global is written to are marked with "*"
+-- typical usage: luac -p -l file.lua | lua globals.lua | sort | lua table.lua
+
+while 1 do
+ local s=io.read()
+ if s==nil then break end
+ local ok,_,l,op,g=string.find(s,"%[%-?(%d*)%]%s*([GS])ETGLOBAL.-;%s+(.*)$")
+ if ok then
+  if op=="S" then op="*" else op="" end
+  io.write(g,"\t",l,op,"\n")
+ end
+end