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 — most relevant 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.