Let a person reopen their own set from the set view after its checks fail #2659

Part of #2422 (F-DSK). Found by the independent review of #2658. This is existing v2 behaviour.

When a person's set fails its checks, or is recovered from a check job that ended, the problem text says to reopen it and submit it again. The set view offers only Reject on a set in checks failed. Reopening exists only as the agent tool reopen_change_set, so a person's own set has no way forward from the set view.

Scope

• The set view offers "Reopen" on a set in checks failed to the person who opened it. It moves the set back to open, as the agent tool does.
• The handler applies the same state and opener rules as the panel.
• Tests: a person reopens their failed set and submits it again. An agent's failed set offers no Reopen to a person.

Acceptance

• A person whose set failed its checks can reopen it from the set view and submit it again.