Add Playwright tests and Vitest coverage thresholds for SDK

[AugistineCreates]

This pr closes #254

Add Vitest coverage thresholds (≥ 70 % for statements, branches, functions, and lines) to the SDK and wallet packages, integrate the thresholds into the CI pipeline, and add a Codecov badge to the root README.

Changes included

• Updated sdk/vitest.config.ts and frontend/wallet/vitest.config.ts with coverage settings and thresholds of 70 % for statements, branches, functions, and lines.
• Modified CI workflow (.github/workflows/ci.yml) to run Vitest with coverage and fail the build if any threshold is not met.
• Added frontend/wallet/vitest.config.ts (new) and updated sdk/vitest.config.ts (new content) to enable coverage collection.
• Added frontend/wallet/package.json and sdk/package.json scripts for running tests with coverage.
• Added sdk/playwright.config.ts, sdk/tests/browser-matrix.spec.ts for browser‑matrix testing.
• Updated README.md with a Codecov badge showing current coverage percentage.
• Committed all new files and changes in a single commit on branch coverage‑thresholds.

This PR brings automated coverage enforcement to prevent future coverage regressions and provides a visible badge for the project’s health.

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[Miracle656]

Thanks for tackling the coverage gate (#254) and browser matrix (#253). A few blocking issues need to be resolved before this can land:

1. This branch is based on main from before #315 merged, and it reverts that work. The sdk/package.json diff removes the ./react export subpath and the @tanstack/react-query peerDependency that #315 added. Merging this would break the just-landed wagmi-style hooks. Please rebase onto the latest main.

2. .github/workflows/ci.yml indentation is broken. The new steps (- name: Run Vitest coverage, etc.) are indented 4 spaces, but the existing steps in that job are at 6 spaces — so they're misnested and the workflow is invalid YAML. They need to line up with the surrounding - run: steps.

3. Jest vs Vitest mismatch. The SDK's tests run on Jest ("test": "jest", jest config, ts-jest). Adding vitest run --coverage with a hard 70% threshold will run against a different (or empty) test set and fail. Either compute coverage from the existing Jest setup (jest --coverage + coverageThreshold), or migrate the suite to Vitest deliberately — but don't run both.

4. The browser-matrix test is a no-op. page.evaluate(() => typeof useInvisibleWallet === 'function') references a Node-side import inside the browser page context, where it's undefined — so it doesn't actually exercise the WebAuthn happy-path, and will likely fail. Also webServer.command: 'npm run dev' has no corresponding dev script in sdk/, so Playwright can't boot the server. The matrix needs a real page that loads the bundled SDK and runs the happy-path.

5. fail_ci_if_error: true on the Codecov step requires a CODECOV_TOKEN secret that isn't configured — this will fail CI on its own.

Once it's rebased and the CI/test wiring actually runs green, I'll re-review. Thanks!