Fixed a mentor profile bug: availability was hardcoded, not real

A mentor profile's "Mentor Available" tag was literally hardcoded text. It showed the same thing regardless of whether that mentor was actually still accepting requests. It now reflects the real value, and shows "Not currently accepting requests" when that's actually true. That matters most if you land on a profile from an old link or a search result.

Mentor profiles also now show a real "Verified Mentor" badge, backed by our actual approval check rather than being purely decorative.