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/xd.lua

@@ -0,0 +1,14 @@
+-- hex dump
+-- usage: lua xd.lua < file
+
+local offset=0
+while true do
+ local s=io.read(16)
+ if s==nil then return end
+ io.write(string.format("%08X  ",offset))
+ string.gsub(s,"(.)",
+	function (c) io.write(string.format("%02X ",string.byte(c))) end)
+ io.write(string.rep(" ",3*(16-string.len(s))))
+ io.write(" ",string.gsub(s,"%c","."),"\n") 
+ offset=offset+16
+end