fix(web): clean up React tests globally

[swear01]

Summary

• Add explicit React Testing Library cleanup in the shared web Vitest setup.
• Prevent React work from leaking past jsdom teardown when tests use render/renderHook without local cleanup.

Root cause

web/vitest.config.ts uses globals: false, so React Testing Library's auto-cleanup is not reliably registered through the usual global hook path. A few web tests render React components/hooks without local cleanup(), leaving scheduled React work alive after jsdom has already removed window. On upstream main (b44885a), this surfaced in CI as Vitest unhandled ReferenceError: window is not defined errors after all web tests had otherwise passed.

Testing

• bun run test:web -- src/hooks/useThemeColors.test.ts
• bun typecheck && bun run test