GpxStore#save converts eagerly, so "cached" is true for nearly every
file in the tree already — badging that was just noise. Flipped to
PENDING_ICON, shown only for the rare case: a .gpx/.fit dropped
straight into data/gpx/ on the filesystem, bypassing the app, and not
yet opened.
Also add an explicit download button next to delete (DOWNLOAD_ICON) —
the file name itself has been a download link since the last commit,
but isn't obviously clickable at a glance.