fix: word a CronJob's failing run as its last run, and say what points to a cause - #590

A CronJob's own scheduled Job creation is no longer listed under "In the last 30 minutes"; the line appears only when something else changed. The check is by ownership in the model, so a Job someone else created in the namespace is still named.

An update about a CronJob's failing run now reads "Its last run, job X, failed: <the run's own failure text>." instead of "It is spreading to job X: it is failing: ...". The failure text comes from the run's finding, so the count is never fixed in the wording.

"nothing outside it explains this" becomes "nothing outside it points to a cause". The sentence is built from the upstream kinds the solver reached, but it is also reached when candidates were weighed and dropped, or when the checked list is empty, so it cannot promise that nothing explains the failure.

Scenario message goldens (78) change only by that phrase, except cron-runs-keep-failing. SCORECARD totals and the ratchet are unchanged.