[codex] Upgrade stack and harden compare UI

[kpoxo6op]

What changed

This PR upgrades the app to a current pinned Next/React/Tailwind toolchain, migrates the repo to pnpm, fixes the compare experience regressions, and adds CI/browser tests so those regressions are harder to reintroduce.

Why

The site had several UI regressions around the compare page and header layout, and the repo was still on an older package/tooling setup. The goal here was to modernize the stack, stabilize the compare behavior, and put automated checks in place so future changes are less likely to break the site silently.

Highlights

• upgraded core app/tooling dependencies and moved to pinned pnpm
• migrated ESLint config to the flat config format
• updated the app for current Next.js behavior and build requirements
• fixed compare slider behavior, URL sync, alignment, mobile safe margins, and header spacing
• configured Vercel to build consistently with pnpm@10.33.0
• excluded local env files from Vercel uploads
• added Playwright e2e coverage and GitHub Actions CI
• added AGENTS.md with repo-specific rules for future agent work

Root causes addressed

• compare regressions were caused by brittle slider/render wiring and mismatched geometry between the visible control and the image reveal boundary
• Vercel preview failures were caused by outdated project Node settings and a client-side useSearchParams() pattern that broke prerendering in Next 16
• package-manager drift and missing CI allowed changes to land without strong browser-level verification

Validation

• corepack pnpm lint
• corepack pnpm typecheck
• corepack pnpm build
• corepack pnpm test:e2e
• Vercel preview deployment succeeded with pnpm v10.33.0

Preview

• https://thennow-ixzxp9drt-kpoxo6ops-projects.vercel.app
• https://thennow-kwg7b9p71-kpoxo6ops-projects.vercel.app

[vercel]

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Project	Deployment	Actions	Updated (UTC)
thennow	Ready	Preview, Comment	Apr 20, 2026 7:01am