Filter lessons by term

Update the query "lessons" to accept an optional "term" argument.

If provided we need to return only lessons that match that term on the lesson "title"

Start at the `lessons` query entry point and inspect how its arguments and lesson results are handled. Add the optional `term` behavior so results match the term in the lesson title, while omitting it preserves the existing results; verify both cases with the available query checks.

Written by the indexing model from the issue text.