Mentor profiles now show session format and real response times

Choosing a mentor works better when you know what working with them will actually be like. Mentor profiles now show two more things.

First, session format: whether a mentor prefers video calls, async text mentoring, or is happy with either -- straight from the preference mentors set themselves. You can also filter your matches by format on the Find a Mentor page, and it factors into who we recommend.

Second, response expectations: once a mentor has responded to at least five requests, their profile shows their typical (median) response time, computed from real history. Until then it honestly says "No response data yet" -- we will never invent a number to make someone look responsive.