[devin-ai-integration]

Summary

Completes the Angular 9 → React 19 + TypeScript (Vite) migration of the HN PWA and cuts over: Angular is removed, CI moves from Travis to GitHub Actions, and Firebase Hosting now serves react-app/dist.

Starts from the integrated react-app/ in #927 (which ports all features but stops before cut-over). This PR overlaps/supersedes #922–#927; only one should land.

On top of #927's react-app/:

• Playbook layout: src/api → src/services, src/features → src/pages (imports updated, no behaviour change).
• react-router-dom 6.30 → 7.18 (clears the v6 Snyk advisory); removed the v6 future flags (ROUTER_FUTURE_FLAGS), which are the v7 defaults.
• Playwright e2e (react-app/e2e/, replaces the Protractor spec): app shell + no console errors, all 8 routes, header/footer nav, item/user/error pages, theme persistence + settings popup, PWA precache / Angular ngsw retirement, offline deep links. Runs against vite build + vite preview with the HN APIs mocked. 29/29 pass locally.
• CI/CD: .travis.yml (Node 6, Angular CLI) → .github/workflows/react-app-ci.yml (lint, prettier, tsc -b, Vitest, build, Playwright) and react-app-deploy.yml (Firebase deploy on master, skipped when no FIREBASE_SERVICE_ACCOUNT/FIREBASE_TOKEN secret).
• firebase.json: hosting.public: "react-app/dist", SPA rewrite limited to route-like URLs (missing static files still 404), immutable caching for hashed assets, no-cache for index.html, sw.js, ngsw-worker.js, manifest.
• Cleanup (only after the checks below passed): removed src/, e2e/, angular.json, tsconfig*.json, karma.conf.js, tslint.json, ngsw-config.json, browserslist, yarn.lock; root package.json now has no deps and just forwards dev/build/test/lint/typecheck/e2e to react-app/.
• README / CONTRIBUTING / react-app/README.md rewritten for the React stack.

Things to know before merging

• User profiles come from https://api.hnpwa.com/v0/user/{id}.json, carried over from React port: integrated react-app/ (foundation + feeds, item/comments, user, shell) #927, because node-hnapi's /user/:id returns 404. On master, /user/pg currently shows "Could not load user pg." (see the side-by-side below). Feed and item endpoints are unchanged.
• The legacy Universal Analytics snippet (UA-66348622-3) is ported as-is from Angular. UA has been shut down, so it's a no-op, same as on master.
• The first deploy needs a Firebase secret on the repo/production environment. Until one is added the deploy job just logs a notice.

Verification

• react-app: npm run lint, format:check, typecheck clean; Vitest 127/127; vite build OK (13 precache entries); Playwright 29/29; npm audit 0 vulnerabilities.
• Side by side with the Angular app (master, ng serve on :4300) against the live API at 1280px and 390px: feeds in all 3 themes, item + comments, settings popup, mobile item header. The only difference was the user page (see above).

React app (/news/1):

Angular (left) vs React (right):

Devin-Org: engineering

Link to Devin session: https://devin-gtm.devinenterprise.com/sessions/f9c8ac375ddf4a1c9fc6ace52b5c5c21
Open in Devin Desktop: https://devin-gtm.devinenterprise.com/desktop/session/f9c8ac375ddf4a1c9fc6ace52b5c5c21?variant=devin
Requested by: @ishita-cog

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