[BUG] check for arc / git intactness

[Brilator]

It is possible to open ARCs without a .git folder. This happened a lot with some of the recent ARCitect releases, where the shipped git might have been an issue.

Since this creates downstream issues (not being able to do anything git; commit, sync, add branches, remotes, etc.), I would suggest to prompt a warning when opening such an ARC (something like "ARC is not intact. No .git detected.") and then disable git-related views Commit, DataHUB sync, History.
I would not suggest to disallow working on such ARCs.
If I remember earlier discussions correctly, git is not a MUST (i.e. ARC could be shared / version-controlled via alternatives).

[Brilator]

Related error: message parsed to branch name is cut off "(fa)tal"

[JonasLukasczyk]

Will be addressed with #225