BE-4: Upgrade Next.js 12 to 14

[devin-ai-integration]

Summary

Upgrades the Next.js framework from v12.1.0 to v14.2.x (resolved to 14.2.35), along with all required companion upgrades. The pages/ directory routing is fully preserved — no App Router migration.

Package changes:

• next: 12.1.0 → ^14.2.0
• react / react-dom: 17.0.2 → ^18.2.0 (required by Next.js 14)
• eslint-config-next: 12.1.4 → ^14.2.0
• Removed @babel/core and @babel/preset-react (no longer needed)

Code changes:

• Deleted .babelrc to enable SWC compiler (Next.js 14 default). The config only contained @babel/preset-react, which SWC handles natively.
• Added legacyBehavior prop to 5 <Link> components that wrap non-text children (<button>, <div>), since Next.js 13+ changed Link to automatically render an <a> tag.

Unchanged:

• pages/ directory routing, getServerSideProps, getStaticPaths, getStaticProps — all still fully supported
• next.config.js — no changes needed (swcMinify is default in 14)
• No next/image migration needed (app uses plain <img> tags)

Build and lint pass. All lint warnings are pre-existing (img alt text, useEffect deps).

Review & Testing Checklist for Human

• Verify next-sanity-image works at runtime — this package declares peerDependencies: next@^11 || ^12, so --legacy-peer-deps was required during install. Confirm Sanity image rendering still works on product pages and banners.
• Smoke-test the app in a browser — run npm run dev and verify: homepage loads with products, product detail pages render, cart interactions work, and the success page renders correctly. React 18's automatic batching and stricter StrictMode (double-firing effects in dev) could surface subtle issues.
• Verify Link navigation — click through all links (product cards, banner CTAs, "Continue Shopping" buttons in cart and success page) to confirm legacyBehavior preserves the expected behavior.
• Test Stripe checkout flow if possible — the payment API route and client-side redirect are untested in this upgrade.

Notes

• Pre-existing lint warnings (missing alt props on <img>, missing useEffect deps) were intentionally not addressed — they are unrelated to this upgrade.
• yarn.lock was not updated since the project uses npm / package-lock.json.

Link to Devin session: https://app.devin.ai/sessions/62188216545d4df1881756c5941a963e
Requested by: @Colhodm

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.