Add an optional lba alias during install

[Lingbou]

Summary

It would be convenient if the installer created a short lba alias that points to the installed libra binary.

Why

libra is a bit longer to type than git. A short local alias like lba would make day-to-day CLI usage faster without renaming the project.

Possible behavior

During install, create lba next to libra in the install bin directory, for example:

~/.libra/bin/libra
~/.libra/bin/lba -> libra

This could be automatic, or controlled by an installer flag if preferred.