Fix channel pdf summary output

[MisRob]

Summary

Follow-up to #5540 where we removed Vuetify from channel details page. That caused some errors as well as visual problems in the generated channel summary PDF, particularly for channels with no thumbnail images available.

This PR optimizes the new page implementation to produce the expected PDF output.

Screenshot of one of the channels PDF from my localhost:

Reviewer guidance

• Code: Since this just optimizes very recently added logic, I think that there's no need to compare with the previous version. Perhaps just have a look at it as a whole.
• Testing: I think it would be best to preview pdfs on production-like data for channels and resources with and without thumbnails on the unstable server after we merge.

[LianaHarris360]

Ran it in my local and looked over a downloaded pdf of the channel details, everything looks fine to me, no concerns.

[MisRob]

Okay, thanks for trying it too @LianaHarris360