Turning on a storage retention rule saved 8 days immediately, which could
start a cleanup sweep before the user picked an age. The switch now opens a
local age draft. Only a committed age (blur, Enter, or a step) is saved, and a
failed save returns the rule to off. Leaving, Escape, or switching the draft
off saves nothing, and turning a saved rule off still saves at once.

Fixes #14743

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>