Add CI pipeline, baseline runtime test, and production-readiness guidance

[alexcollins]

Motivation

• Add automated validation and a minimal runtime test so the package is verifiable in CI before publishing.
• Provide practical launch guardrails for teams embedding the voice UX in AI apps to reduce integration surprises.

Description

• Add a GitHub Actions workflow at .github/workflows/ci.yml that runs npm ci, npm run typecheck, npm run build, and npm test on pushes and PRs.
• Add a lightweight runtime test tests/format.test.mjs that exercises formatElapsed from the built dist to provide a dependency-free quality gate.
• Wire npm test in package.json to run the build followed by the runtime test via node tests/format.test.mjs.
• Add a Production Readiness section and a launch checklist to README.md with practical guidance (capability fallback, permission handling, post-processing, cross-browser QA, and a launch checklist).

Testing

• Ran npm run typecheck and the TypeScript checks completed successfully.
• Ran npm run build and the project compiled into dist successfully.
• Ran npm test (which runs the build and the runtime test) and the baseline runtime test passed (format tests passed).

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Codex Task