fix(tui): announcement bullets bleed past dialog border

Nesting <span> children inside <text> made opentui treat each child as
an inline block and skip word-wrapping, so bullets overflowed past the
dialog's right border into the terminal background.

Plain-string children inside <text> wrap correctly. The fix is to
detect whether a bullet has a URL:

- No URL bullets render as a single <text>{string}</text> — opentui
  word-wraps these against the parent box's effective width.
- URL bullets render as <text>{prefix}<a href>{url}</a>{suffix}</text>
  which keeps the URL clickable via opentui's <a> (OSC 8 hyperlink
  in supporting terminals) while still wrapping plain text segments.

Dropped the explicit <u> wrapper since opentui's <a> already underlines
the link. Dropped the bullet-prefix <span> wrapper for the same reason
— it was forcing opentui out of word-wrap mode.

Documented the constraint inline so future edits don't reintroduce the
overflow regression.