feat: TypeScript foundation setup

[devin-ai-integration]

Summary

Sets up TypeScript infrastructure for the Next.js project so subsequent migration sessions can proceed. All existing .js/.jsx files continue to work via allowJs: true.

Changes:

• Installed typescript@5, @types/react@17, @types/react-dom@17, @types/node as devDependencies
• Created tsconfig.json with strict: true and all requested compiler options (Next.js auto-appended target, lib, forceConsistentCasingInFileNames on first build)
• Removed .babelrc and uninstalled @babel/core + @babel/preset-react (Next.js 12 uses SWC by default)
• Created types/index.ts with shared SanityProduct, CartItem, and SanityBanner interfaces derived from the Sanity schemas
• Added next-env.d.ts (generated by Next.js) and *.tsbuildinfo to .gitignore

Version choices:

• TypeScript 5.x (not 6.x): TS 6 deprecates moduleResolution: "node" and errors on it; TS 5 is the latest stable that supports the requested tsconfig without changes.
• @types/react@17.0.39 (not latest): Newer @types/react versions add an exports field that breaks Next.js 12's require.resolve('@types/react/index.d.ts') detection, causing the build to fail. 17.0.x is also the correct match for the project's React 17 runtime.

Verification results:

• ✓ npx tsc --noEmit — no errors
• ✓ npm run build — compiles and generates all pages successfully
• ✓ npm run dev — starts without errors on localhost
• ✓ .babelrc deleted, @babel/core and @babel/preset-react absent from package.json
• ✓ tsconfig.json contains "strict": true
• ✓ types/index.ts exports SanityProduct, CartItem, SanityBanner

Review & Testing Checklist for Human

• Verify tsconfig.json settings are acceptable — Next.js auto-added target: "es5", lib, and forceConsistentCasingInFileNames on top of the requested options. Confirm these additions are fine.
• Confirm TypeScript 5.x is acceptable — TS 6 breaks with moduleResolution: "node". If TS 6 is required, the tsconfig would need moduleResolution: "bundler" instead.
• Confirm @types/react@17 is acceptable — matches the React 17 runtime, but later migration sessions upgrading React may need to bump this.
• Verify types/index.ts matches Sanity schemas — cross-check SanityProduct / SanityBanner fields against sanity_ecommerce/schemas/product.js and sanity_ecommerce/schemas/banner.js.
• Run npm run build and npm run dev locally to confirm the app works end-to-end.

Notes

• @babel/core was listed under dependencies (not devDependencies) in the original package.json. It has been removed from there. @babel/preset-react was in devDependencies and is also removed.
• --legacy-peer-deps was required during npm install due to a pre-existing peer dependency conflict (next-sanity-image expects @sanity/client@^2 but ^3 is installed).

Link to Devin session: https://app.devin.ai/sessions/7bf8288d22994c09befb752ab19d85d5
Requested by: @WesternConcrete

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[devin-ai-integration]

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[devin-ai-integration]

✅ 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.

[devin-ai-integration]

End-to-End Test Results

Ran dev server locally, tested homepage and product detail page in browser, verified TypeScript type-checking.

All 3 tests passed.

Test 1: Homepage renders after Babel removal — PASSED

• Hero banner with "Summer Sale" visible
• "Best Seller Products" heading present
• All 5 product cards rendered (Speaker $56, Smartwatch $99, Cool In-ear headphones $40, Headphones $55, Headphones $99)
• No Next.js error overlay or compilation errors

Test 2: Product detail page (dynamic route + SSG) — PASSED

• Navigated to /product/speaker via product card click
• Product name "Speaker", price "$56", details, images, Add to Cart/Buy Now buttons all visible
• "You may also like" section renders with other products

Test 3: tsc --noEmit — PASSED

npx tsc --noEmit exited with code 0, no type errors.

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Devin session