Revert Template Modification

Undo an in-call test correction — restores system_instructions and any SOP attachment it touched to their pre-correction text, and marks the correction 'reverted' so it can be given again in a fresh test call and re-applied under whatever the reconciliation logic does today, without needing a new template.

404 if the run isn't found/isn't this template's; 409 if it isn't a revertible in-call correction, isn't 'succeeded', or the template has changed since (reverting would discard that later change).