Add Vitest testing infrastructure

[Just-Insane]

Sets up a complete testing stack so contributors can write and run tests as part of their PRs.

What's included

• Vitest as the test runner (reuses existing Vite config, Jest-compatible API)
• @testing-library/react + @testing-library/user-event for component/hook tests
• @vitest/coverage-v8 for V8-native coverage reports (coverage/ is gitignored)
• Standalone vitest.config.ts that excludes Cloudflare/PWA/compression plugins
• src/test/setup.ts that loads @testing-library/jest-dom matchers globally

New scripts

Command	Purpose
pnpm test	Watch mode (dev)
pnpm test:run	Single run (CI)
pnpm test:ui	Browser results UI
pnpm test:coverage	Run + HTML + lcov reports

CI

pnpm test:run is now a required check in quality-checks.yml alongside lint/typecheck/knip.

Example tests (4 files, 34 tests)

Included as working examples for contributors:

• colorMXID.test.ts — basic pure function tests
• common.test.ts — it.each table-driven tests
• findAndReplace.test.ts — algorithmic utility, edge cases
• sort.test.ts — factory functions with lightweight object stubs

Docs

docs/TESTING.md covers: running tests, where to put files, and examples for utilities, components, hooks, and mocking. CONTRIBUTING.md updated to include test:run in the PR checklist.

[github-actions]

Deploying with    Cloudflare Workers

Status	Preview URL	Commit	Alias	Updated (UTC)
✅ Deployment successful!	https://pr-297-sable.raspy-dream-bb1d.workers.dev	b2696f4	pr-297	Mon, 16 Mar 2026 17:48:25 GMT