Snooze by bumping the trigger field, not adding deferred_until

When a reminder system computes from a single timestamp (e.g. last_contacted + cadence), implement defer as bumping that timestamp to today rather than adding a parallel deferred_until column. Saves a schema field, reuses existing freshness math, and pushes the next reminder by exactly one cadence cycle for free. The slight semantic muddiness (the user did not actually contact them) is honest if the dossier surfaces last_contacted as last decision point, and is a great trade for the simplicity.