core: one run that cannot be read takes its whole repository off the page

[nathancrtr]

Outcome

A git failure while reading one run leaves that run out and keeps the rest of its repository on the page.

Why

Since #530 a repository that cannot be read is left out of the inbox, the portfolio and the metrics, and listed as unreadable. The boundary sits at the repository. If one run's summary throws on a git failure, the whole repository is dropped, and every decision waiting in it leaves the inbox with it.

A run whose record is malformed is a different case and is unaffected. It is still shown as a malformed row.

Work

• Put a second boundary at the run for failures that are not a malformed record.
• Show such a run as a row that says it could not be read and why, the way a malformed run is shown, so that it is counted and not hidden.
• Keep the repository-level boundary for failures that are about the repository, such as listing its runs.

Found while reviewing #530. Part of #492.