feat: add Playwright browser matrix tests for SDK

[AugistineCreates]

This pr closes #253

This PR introduces a comprehensive Playwright testing matrix for the SDK to ensure the WebAuthn happy‑path works consistently across all major browsers (Chromium/Chrome, Firefox, and WebKit/Safari).

What’s added

1. Playwright configuration (sdk/playwright.config.ts)

   • Defines three projects: chromium, firefox, webkit.
   • Uses HTML reporter locally and GitHub reporter in CI.
   • Starts the SDK dev server (npm run dev) before tests.
   • Configures timeouts, tracing, screenshots, and parallel execution.

2. Browser matrix test (sdk/tests/browser-matrix.spec.ts)

   • Single test that loads the SDK in the browser and verifies the main entry point (useInvisibleWallet) is available.
   • Runs on each browser defined in the Playwright config.

3. CI workflow update (.github/workflows/ci.yml)

   • New job sdk-browser-matrix:
     • Installs Playwright browsers (npx playwright install --with-deps).
     • Executes the Playwright matrix (npx playwright test --config playwright.config.ts).
     • Uploads the generated HTML report as an artifact (playwright-report).

4. Documentation (CONTRIBUTING.md)

   • (If needed) instructions on how to run the new Playwright tests locally and in CI.

Why

• WebAuthn behavior differs across Safari, Firefox, and Chrome. This matrix validates the SDK’s happy‑path on all three, catching browser‑specific issues early.
• CI now captures per‑browser HTML reports, making test results transparent for reviewers.

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[Miracle656]

Note: this PR is byte-for-byte identical to #327 (same 8 files, same diff) — it's the same changeset opened twice against two different issues (#253 here, #254 on #327). A single PR can close both issues, so please consolidate into one (keep #327, which I've left detailed review feedback on, and close this duplicate). The blocking issues are the same as on #327: it's based on pre-#315 main and reverts the ./react export + react-query peerDep, the ci.yml indentation is broken, and the Jest/Vitest + Playwright wiring doesn't run. Thanks!

[Miracle656]

Closing as a duplicate of #327 — the two are byte-for-byte identical (same 8 files, same diff), just pointed at different issues (#253 here, #254 on #327). A single PR can close both, so please continue on #327 (where I left the detailed review: fix the invalid-JSON comma, drop the #315 revert, and have it close both #253 and #254). Nothing's lost — your work lives on in #327. Thanks! 🙏