If the only thing you're ever putting in the notes is the Trac link, you could wrap the notes in an a href tag, something like this:
The first gives you a shorter link, but will show the word "Trac" whether there's a link there or not. The latter should only show up if there's actually stuff in the notes, but then it'll show the bare URL.
If your notes sometimes have Trac links and sometimes have other text, this will not work so great. In that situation, I'd recommend making a custom data column for your tasks, dedicated to Trac links, and adding that to your TaskTemplate.html (still wrapping it in the a href as above). Then you can use the Notes field for plain notes.