Coding Agent: UUID in branch name

[chrmarti]

Testing #264383

Not sure this is under our control, but the UUID in the branch name doesn't look good. It would be much nicer to either use an LLM-generated short name based on the initial prompt or a random name using word pairs like VS Code's Git extension does when creating a new branch.

[joshspicer]

In this case the branch name was generated by GitHub. So long as the session is originally created in VS Code, we do have a way to change the branch (GH just requires it be prefixed with copilot/)

Right now I use the date for the branch name in these cases, but I really like the idea of the random word pairs

[alexr00]

(added bug label so this gets verified)