feat: add DisputeCardSkeleton with layout parity for first-paint stability (Closes #815)

[waterWang]

Description

This PR adds DisputeCardSkeleton, a loading skeleton that mirrors the final <DisputeCard/> shape so the first paint doesn't jump when dispute data resolves.

Changes

• src/pages/DisputeCardSkeleton.tsx — New component with layout parity against DisputeCard:
  • Header: title shards (2 lines, max-w-[75%]) + badge pill (h-6 w-24 !rounded-full)
  • Content: reason paragraph (2 lines), penalty strip (rounded-md, h-12), deadline row, tally row (2 items), audit accordion trigger
  • Footer: state label shard (text-xs, h-3) + action button shard (h-9 rounded-md)
• src/pages/__tests__/DisputeCardSkeleton.test.tsx — Tests for:
  • Correct test ID and accessible role (role="status", aria-busy="true")
  • sr-only loading message
  • Skeleton shard rendering

Accessibility

• role="status" + aria-busy="true" for screen reader announcement
• sr-only "Loading dispute details…" message
• prefers-reduced-motion honored at the <Skeleton/> level (motion-reduce:animate-none)

Evidence

• Desktop skeleton layout matches DisputeCard structure
• Mobile: all widths use ratios (% / w-*), no fixed px values
• Dark mode: Skeleton component handles theme via Tailwind bg-muted
• Tests pass

Closes #815

[vercel]

@waterWang is attempting to deploy a commit to the Jagadeesh B's projects Team on Vercel.

A member of the Team first needs to authorize it.