feat: add knockout wheel fixture

[chakravartiavinit]

Adds Knockout Wheel, the second version on the Fixtures page: the same tournament tree wrapped around its champion.

Stacked on #122, which introduces the versioned Fixtures page this entry slots into. Review that one first; this branch contains only the wheel.

What it looks like

Tournament decided	Played through the Round of 16
Champion holds the hub under a trophy and a warm halo, and their run from the rim inward stays lit while everyone else recedes.	Undecided slots draw the same shield the bracket uses for a TBD side. No champion, so no trophy, no halo, and nothing dims.

The geometry

The hub is the final. Each round becomes a ring further out, and the teams themselves form the rim, so a 32-team draw is 63 nodes across 5 rings. Every parent splits its angular wedge between its two feeders, halving each level, with a small gap pulling siblings toward their parent so subtrees separate visually. Sibling pairs are joined by an arc at the midpoint radius plus a radial stem to the parent; the hub's two feeders sit opposite each other and get plain radial lines, since an arc between them would be a half circle.

Nothing is hard-coded to a bracket size. rounds.length drives the ring count and radii, so 8, 16 or 32 teams all render without special cases.

Interaction

• Hover a flag for a Tooltip with Round · Teams · Score, and that flag alone stays lit.
• Tap on touch pins the same trace with a label anchored to the flag, since Tooltip is pointer-only by design. Tap again to release.
• Keyboard: one tab stop for the wheel, then arrows follow the geometry — up walks toward the hub, down to a feeder, left/right around the ring.
• At rest the champion's path is lit.

Props

• rounds — outermost round first, each holding half as many matches as the one before.
• initialRound — index of the outermost round to draw. Earlier rounds are dropped and the kept round's own teams become the rim, so 2 on a 32-team draw opens at the quarter-finals. Defaults to the whole tree.

The Match / Round types are a local copy of the bracket's rather than an import: importing would make the registry bundle the entire bracket into @beui/knockout-wheel. They stay structurally compatible, so one tournament object feeds both components.

Accessibility

role="img" prunes the svg's descendants, so every result is restated in an sr-only list of named lists — deliberately not <section aria-label>, which would add five landmarks competing with real page navigation. Focus uses ring-foreground rather than the --ring token, which is a 10% white hairline that disappears over a flag.

Notes for review

Two things worth knowing about, both verified rather than assumed:

• Hydration. Math.sin / Math.cos are implementation-defined in their last digits, so Bun's SSR and the browser disagreed on every derived coordinate and React reported a mismatch on each one. polar() now quantizes to 3 decimals, far below sub-pixel at a 760-unit viewBox.
• Flag loading. SVG <image> has no loading="lazy", so 63 requests fired on mount. They're now gated behind useInView: 0 requests off-screen, 63 once the wheel approaches the viewport.

Below 32rem the wheel holds its size and pans inside its own scroll container, the same pattern KnockoutBracket uses — letting it shrink put 32 rim flags at 21px, too small to tell apart or tap.

Checks

bun run check (typecheck, lint, registry) and bun test pass — 41 tests, 53 registry components. Verified in the browser across pointer, touch and keyboard, in both themes, and under prefers-reduced-motion.