Test suite exists but is never run in CI or locally (no test runner installed, no test script)

[abayomicornelius]

vitest.config.ts and 15+ test files (e.g., src/utils/format.test.ts, src/components/SendFlow/AmountStep.test.tsx) exist in the repo, but package.json has no test script and no vitest, @testing-library/react, or jsdom in devDependencies. None of the four workflows in .github/workflows/ (ci.yml, lint.yml, typecheck.yml, preview.yml) invoke tests, so the suite silently bit-rots with no signal when it breaks.

Add the missing dependencies, a "test": "vitest run" script, and a CI job that runs it.