Add view transitions eval (agent-043) (#92260)
## Summary
- Adds `agent-043-view-transitions`, a new eval that tests whether
agents can add React View Transitions to a Next.js product gallery app
- Starter app is a simple product list/detail gallery with Suspense
boundaries, no view transitions
- EVAL.ts checks 8 patterns: `viewTransition` config flag,
`ViewTransition` imported from `react`, shared element `name` props,
`transitionTypes` on Link, Suspense enter/exit animations,
`default="none"` isolation, `prefers-reduced-motion` CSS, and
`::view-transition-*` CSS pseudo-elements
## Test plan
- [x] Starter app builds with `next build`
- [x] All 8 EVAL.ts tests fail on unmodified starter (no false
positives)
- [x] All 8 EVAL.ts tests pass on a correct golden solution
- [x] Golden solution builds with `next build` (viewTransition
experiment detected)
- [x] Commit passes lint-staged (prettier + eslint)
