Mixed composer attachment rail

selection order: poem.txt > reference-1.png > reference-2.png > reference-3.png > reference-4.png > reference-5.png > reference-6.png > reference-7.png > reference-8.png > reference-9.png > reference-10.png
one attachment group: true
all cards share one row: true
every card is 64px high: true
the file card is wider than an image: true
overflowing cards scroll horizontally: true
the rail does not wrap: true