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/table.lua

@@ -0,0 +1,12 @@
+-- make table, grouping all data for the same item
+-- input is 2 columns (item, data)
+
+local A
+while 1 do
+ local l=io.read()
+ if l==nil then break end
+ local _,_,a,b=string.find(l,'"?([_%w]+)"?%s*(.*)$')
+ if a~=A then A=a io.write("\n",a,":") end
+ io.write(" ",b)
+end
+io.write("\n")