[Feature]: Add no-JS fallback for library/download views (support legacy kindle browser)

[su77ungr]

Before submitting

• I searched existing issues to avoid duplicates

Problem

Thanks for the work so far. I found running the calibre-server extremely useful for downloading docs via the kindle's web browser
AFAIK your frontend will not work on my kindle (pw gen 6) - so adding a fallback for the download section would be great so converted files can be downloaded to the kinlde directly

Proposed solution

add non-JS fallback

Additional context (optional)

No response

[NilsLeo]

I will look into this at some Point. Thank You!