Mentor profiles now show when details were last confirmed

Every mentor on Designed periodically confirms that their profile details -- role, employer, availability, capacity, and topics -- are still current. Until now that confirmation was invisible: mentors did it, but nobody browsing could tell.

Mentor profiles now show a small "Details confirmed current" date right under the mentor's role and employer. A recent date means the info was just re-attested; an older one is honest signal too. Mentors see the same date on their own Settings page, labeled with exactly where it appears publicly, and the periodic confirmation prompt now spells out everything it covers.