The reading-list cover badge previously read "Reading List · 1" when a
featured entry existed and "Reading List · 0" otherwise — a binary
flag stamped onto a count format. The user's actual reading list can
hold many entries, and the design clearly intends the badge to show
the total ("Reading List · 5" in the mock).
Pass snapshot.reading_list.len() through render_reading_list_cover so
the badge mirrors the real count.