Move SDK DOM progress indicator into the app (#231)

[yunus-dev-codecrafter]

closes #231

What changed

Moved the SDK's imperative DOM-based progress indicator out of the headless @sharibo/client and rebuilt it as a React component (app/src/components/ArtifactProgress.tsx) that subscribes to the existing subscribeToArtifactPrefetch API, announces progress through the app's shared usePoliteLiveRegion hook, and renders a token-styled progress bar. Also deleted the installIndicator/updateIndicator DOM code, exported the subscription API surface, and resolved a pre-existing prefers-reduced-motion merge conflict in style.css.

Why

Closes #231

The SDK's packages/client/src/artifacts.ts hand-built a DOM node (hardcoded colors, its own aria-live region, fixed positioning) inside an otherwise headless SDK, so it couldn't follow the app's theme, respect prefers-reduced-motion, or be positioned by the app. Moving the indicator into the app makes the SDK fully headless and reuses the app's single live region.

Testing

• Circuit tests (cd circuits && npm test)
• Contract tests (cd contracts && cargo test)
• E2E against testnet (npm run e2e)
• App tests added (cd app && npm test src/components/ArtifactProgress.test.tsx — 3 passing)
• Live-region guard verified (SDK has no document. references; exactly one aria-live region in the rendered app)
• Docs-only (no code changed)

Screenshots

The progress bar now renders inside the app card using existing design tokens (--accent2, var(--border), JetBrains Mono), showing "Preparing prover… N%" with an animated fill; it hides automatically once artifacts are ready.