v0.5.1

v0.5.1 — captions read as one line

A sentence spanning two turns was drawn as two pills at two different sizes
with a gap between them. The previous turn is now the dimmed lead-in of the
same block as the live text, at the same size, so it reads as running text.
Both share one character budget, so the caption block never outgrows a single
caption's worth. In "Both" mode the lead-in is tracked per source, so one
speaker's text can no longer attach to the other's caption.