v0.5.180

What's new

The send button no longer looks broken when the composer is empty. The
disabled state applied both opacity: 0.3 and a saturate(0.4) filter —
carried over from the old wide "Send" pill, which could afford to grey out hard
because it had a text label. On the new bare icon circle the arrow is the only
thing there, so the double treatment washed it into grey mush that read as a
dead control rather than one waiting for input.

It now dims to opacity: 0.45 with no desaturation, so the empty state keeps
the accent blue and crisp edges. Measured on the rendered pixels: disc
saturation up from 0.30 to 0.53, arrow contrast up from 46 to 71.

The arrow's shape is unchanged — it was always identical to the design.

Full Changelog: v0.5.179...v0.5.180