ProviderSnapshot stored a numeric resetsAt as its epoch digits, while every
later reader parses that field as a date string: the popup countdown through
ResetPresentation, the panel "resets within" rule through Date.parse, and the
private-mode timestamp projection. A provider reporting a numeric reset date
therefore printed the raw milliseconds instead of a countdown and never
satisfied the reset visibility rule, even though ProviderSnapshot and
ResetPresentation both already accept numeric dates on the resetValue path.

Normalize a numeric reset date to its ISO form when the row is built, out of
range and non-finite values keeping the existing empty reset, and pin the
behavior in tst_provider_snapshot.

Documentation: CHANGELOG Unreleased and the ProviderSnapshot notes in
docs/development.md.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>