Cleaned up a handful of rough edges on mentor profiles

A pass through real mentor profile data (not sample data) turned up a small set of real, live rendering bugs:

On profile pages with no current job, the role tagline below a mentor's name was rendering as an empty heading instead of falling back to their listed job title. The "My Career" and "My Education" sections had a similar issue — the section heading was written inside the list loop itself, gated on being the first item, so a mentor whose first career or education entry was incomplete could lose the heading for the whole section, or in rarer cases render it more than once. Both sections now filter their entries up front and render the heading once, only when there's something to show under it.

Every mentor and mentee avatar site-wide also had broken alt text — a copy-paste slip meant the literal text "{first_name}" (curly braces and all) was being set as the alt attribute, instead of the person's actual name. Invisible in normal browsing since alt text only shows up when a photo fails to load, but a real accessibility and broken-image bug all the same. It now reads "so-and-so's profile photo," or falls back cleanly when a name isn't available.

Separately, we confirmed Critique's example content was already clearly and consistently labeled as sample data throughout — nothing there could be mistaken for a real member's activity, so no changes were needed there.

Third entry in the ongoing pass through the platform's public-facing trust and reliability issues.