fix: add qualified capi lua descriptor alias

[Sunrisepeak]

Summary

• Add a qualified descriptor alias for mcpplibs.capi.lua so mcpp 0.0.29/0.0.30 resolve the Form A package descriptor before falling back to compat.lua.
• Keep the descriptor content identical to the existing canonical pkgs/c/capi.lua.lua entry.

Test plan

• Verified the alias file matches pkgs/c/capi.lua.lua.
• Verified descriptor contains spec/name/xpm fields with a local Python shape check.
• Local lua5.4 is not installed; GitHub validate workflow will run the Lua syntax check.