Opening a doc on its page never set FileGroup.viewed, so docs were missing
from Recently Viewed. GET /api/docs/:id now marks the doc viewed, with the
same skip_viewed parameter as archives and videos.
The file preview marked a file viewed more than once: opening from a
?preview= URL sent two tracked requests, and every tag change re-fetched the
file with tracking on. The fetches now skip tracking, and the preview marks
each opening viewed once.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
