fix(tui): announcement crashed with 'Orphan text error' on URL line

opentui's <a> and <span> are inline span-like elements that must have
a <text> parent. The previous commit (af11bc4) put <a> directly inside
<box flexDirection='row' flexWrap='wrap'>, which threw:

  Orphan text error: 'https://discord.gg/F2uWxjGnU' must have a <text>
  as a parent: box-90 above a-1

Fix: render each bullet as a single <text> element with inline <span>
and <a> children. The bullet prefix '  • ' becomes a muted <span>,
plain segments become default-colored <span>, and the URL becomes an
underlined <a href> — all inline within one <text>, which is what
opentui requires for span-like children.

Documented the constraint in a comment so a future refactor doesn't
re-introduce the same orphan-text crash.