Add strong indication when development build completes

Ideally a big green log, or maybe even a sound.

Since the snaps-beta is live, we have more devs than ever running development builds of MetaMask, and not knowing when the build is complete is a recurring point of confusion.

The issue does not name files, commands, or tests. Start by locating the development-build workflow and its existing completion output; clarify whether a prominent green log, a sound, or both is wanted, then define completion as an unmistakable signal that can be verified while running a development build.

Written by the indexing model from the issue text.