Restore analytics bootstrapping in Next apps

[PavelMakarchuk]

Summary

Restore GA4 and Vercel analytics bootstrapping in the Next.js website and calculator app layouts.

Root cause

The legacy Vite apps loaded GA and mounted Vercel Analytics, but the migrated Next app layouts did not. That left window.gtag undefined on migrated routes and caused analytics to drop sharply once traffic shifted to those apps.

Changes

• load gtag.js in website/src/app/layout.tsx
• initialize window.dataLayer and window.gtag in website/src/app/layout.tsx
• mount @vercel/analytics and @vercel/speed-insights in website/src/app/layout.tsx
• load gtag.js in calculator-app/src/app/layout.tsx
• initialize window.dataLayer and window.gtag in calculator-app/src/app/layout.tsx
• mount @vercel/analytics and @vercel/speed-insights in calculator-app/src/app/layout.tsx

Verification

• ran local Next dev servers via bun run dev
• verified served HTML for http://localhost:3002/us includes GA4 bootstrap and Vercel analytics clients
• verified served HTML for http://localhost:3002/us/pe84 includes GA4 bootstrap and the migrated AppClient route bundle used for tool_engaged
• verified served HTML for http://localhost:3003/us/simulations includes GA4 bootstrap and Vercel analytics clients

Notes

• local calculator routes still surface an unrelated existing SSR issue: No QueryClient set, use QueryClientProvider to set one
• that issue is separate from this analytics fix and does not change the restored analytics bootstrapping

[vercel]

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Project	Deployment	Actions	Updated (UTC)
policyengine-app-v2	Ready	Preview, Comment	Apr 15, 2026 2:53pm
policyengine-calculator	Ready	Preview, Comment	Apr 15, 2026 2:53pm
policyengine-calculator-next	Ready	Preview, Comment	Apr 15, 2026 2:53pm
policyengine-website	Ready	Preview, Comment	Apr 15, 2026 2:53pm

[policyengine]

This PR correctly restores analytics bootstrapping in the Next.js apps. The implementation is solid and matches the legacy Vite app pattern:

What's correct:

• ✅ GA4 measurement ID (G-2YHG89FY0N) matches the legacy HTML files
• ✅ Uses Next.js Script component with proper strategy (afterInteractive)
• ✅ Assigns window.gtag globally for downstream code compatibility
• ✅ Analytics and SpeedInsights components properly mounted in body
• ✅ Dependencies (@vercel/analytics, @vercel/speed-insights) available in root package.json
• ✅ Both calculator-app and website layouts updated consistently

Verification:
The legacy Vite apps (app/calculator.html, app/website.html) have the same GA4 bootstrap script, and the main entry files (main.calculator.tsx, main.website.tsx) mount Analytics/SpeedInsights components. This PR correctly ports that pattern to the Next.js layouts.

No issues found. The implementation will restore window.gtag and analytics tracking on migrated routes.