The 2fa.codes_fresh reveal flag is now a timestamp (set at enrollment) and
RecoveryCodes::mount() only reveals within [now-600s, now], symmetric to the
download-grant window. A reveal flag whose modal never opened can no longer
re-reveal the codes later in the session. FirstFactorCodesTest asserts the
flag is an int.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>