MBA-2247: Migrate angular2-hn to React + TypeScript

[devin-ai-integration]

Summary

Rebuilds the Hacker News PWA in React with feature parity, as a self-contained app under react/ (Vite + React 18 + TS strict + react-router v6 + vite-plugin-pwa + Vitest). No Angular files are modified or deleted — both implementations live side by side.

Key mappings from the Angular app:

• Routes mirror app.routes.ts: / → /news/1; /{news,newest,show,ask,jobs}/:page → FeedPage; /item/:id and /user/:id are React.lazy-loaded (parity with Angular lazy modules).
• HackerNewsAPIService → typed fetch client (src/api/hackerNewsApi.ts) with AbortController cleanup in useEffect; poll items fetch options id+1..id+n via Promise.all and compute poll_votes_count.
• SettingsService → SettingsProvider/useSettings() context with the same localStorage keys (theme, openLinkInNewTab, titleFontSize, listSpacing) and the same prefers-color-scheme fallback behavior when no theme is saved.
• Theme engine (Default / Night / AMOLED Black): global SCSS ported essentially verbatim (not CSS modules) because _themes.scss cascades from a theme class onto global class names (.wrapper, .subtext, …); the app shell renders <div className={settings.theme}> exactly like app.component.html.
• CommentPipe → formatCommentCount() util; recursive Comment component with collapse and deleted states.
• PWA: vite-plugin-pwa (generateSW) with ported manifest and icons, precaching the app shell + assets to mirror ngsw-config.json.
• Tests: Vitest + React Testing Library (8 tests: util, settings context, Comment, Item, FeedPage, App smoke test replacing the protractor e2e).

Verification

In react/: npm run lint, npm run build (tsc --noEmit + vite build), npm test -- --run all pass; vite preview serves the app.

Devin-Org: engineering

Link to Devin session: https://app.devin.ai/sessions/164e49519e9e4ee48c749f721bc49d48
Open in Devin Desktop: https://app.devin.ai/desktop/session/164e49519e9e4ee48c749f721bc49d48?variant=devin

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring