fix: keep Start breadcrumb label visible in subfolders on mobile - #509

The root crumb renders icon-only below the force-icon-text breakpoint, so
the label had no text node to attach to and the crumb was blank but still
clickable. Move it to the button wrapper, which exists in both render paths.

The UploadPicker form inherits height from --default-clickable-area (48px)
while the themed button is 40px, making it the tallest flex item in the
header. Views with the "New" button rendered 4px taller, shifting the
breadcrumb and grid toggle 2px down compared to Favorites and Deleted files.

Views without "New" still render an empty placeholder div that consumes one
of the header's 4px gaps, pushing their breadcrumb out of line with the
row-name column.