All transitions use cubic-bezier(0.23, 1, 0.32, 1) instead of the
default ease; the attention button also fades its hover shadow.

Fix a real ring bug found comparing dark/light screenshots: the
focus rule (.tab-page.split .pane.focused, four classes) outranked
every attention ring (two), so a focused pane needing triage showed
the accent ring instead of its severity colour. Focus drops to two
classes, rings rise to three, and the hierarchy is documented in
the comments.

Co-Authored-By: Claude Code <noreply@anthropic.com>