Mara reported the rebuild spinner rendered as a rotating L-corner
('_|' / '⌐') instead of a smooth orbiting arc. Two issues:
1. The previous version coloured TWO adjacent border sides amber
(border-top + border-right). With the rest of the border
transparent, this paints a sharp L-shape at the icon corner —
which when rotated reads as a spinning border-corner, not a
loading spinner.
2. @keyframes had only `to` defined. Safer to include explicit
`from { transform: rotate(0deg) }` so any browser that doesn't
default cleanly still picks up the rotation.
Fix is the classic CSS spinner shape: faint amber ring around the
full icon perimeter (`border: 2px solid rgba(250, 179, 135, 0.2)`)
with one brighter top arc (`border-top-color: var(--amber)`) that
rotates. Reads unambiguously as a loading indicator.
Closes#804.
dc8c71c687