CI integration

[vemv]

Context

It is desirable that PRs are already formatted and comply with the linters.

Task

Implement a CLI task that formats/lints stuff, failing the CI build when stuff is wrong.

Acceptance criteria

• formatters should have a dry-run option
• formatters should return ok?
• linters should return ok?
• an invokable f-s.ci/-main function should be offered

[thumbnail]

As noted in #93, this issue is best to be picked up after the reporter is available for the whole stack.

This issue could be implemented initially for just the linters, adding the formatters after #110 is done.