Migrate EOL Angular 9 stack to Angular 20 LTS toolchain

[devin-ai-integration]

Summary

The entire toolchain was End-of-Life (Angular 9, TypeScript 3.7, Node 12 types, TSLint/codelyzer, Protractor, RxJS 6). This migrates the app to the current Angular 20 LTS stack and modern, supported tooling. The app builds, lints, and unit-tests clean on Node 20.

Dependency bumps (package.json)

• @angular/* (incl. devkit/cli/compiler-cli/language-service) ~9.0.x → ^20.3.x
• typescript ~3.7.5 → ~5.9.2, rxjs ~6.5.4 → ~7.8.0, zone.js ~0.10 → ~0.15, tslib ^1.10 → ^2.3, @types/node ^12 → ^20.19
• Removed now-unneeded deps: rxjs-compat, node-fetch (unused in src/), ts-node, @types/jasminewd2, jasmine-spec-reporter, karma-coverage-istanbul-reporter

Build system

• Switched from the legacy webpack @angular-devkit/build-angular:browser builder to the modern esbuild-based @angular/build:application builder (angular.json rewritten). Polyfills moved into angular.json (["zone.js"]); src/polyfills.ts and src/test.ts removed (handled by the new builders). Service worker now configured via serviceWorker: "ngsw-config.json" on the production config. Output is now dist/angular-hnpwa/browser/ and still emits ngsw-worker.js.

Lint: TSLint + codelyzer → ESLint (@angular-eslint)

• Deleted tslint.json; added eslint.config.js (flat config) and switched the lint builder to @angular-eslint/builder:lint. A few opinionated rules are intentionally disabled to preserve this app's existing architecture (prefer-standalone, prefer-inject, prefer-control-flow) and two template a11y rules (click-events-have-key-events, interactive-supports-focus) left for a separate a11y pass. All other recommended rules pass.

E2E: Protractor → Playwright

• Removed e2e/protractor.conf.js + the Protractor spec/PO/tsconfig; added playwright.config.ts (boots npm start via webServer) and migrated the smoke test to e2e/app.spec.ts (asserts the app shell + header nav render). e2e script is now playwright test.

Unit tests / Karma

• Updated to current Karma 6 + Jasmine 5 (karma.conf.js rewritten for the @angular/build:karma builder, dropping the old @angular-devkit/.../plugins/karma require). Added a ChromeHeadlessNoSandbox launcher for CI. Added a small comment.pipe.spec.ts so the harness exercises a real test (3 passing).

Required Angular 20 code changes

• Standalone is the v17+ default for declarables, but this app keeps NgModules — so standalone: false was added to every @Component/@Pipe decorator.
• RxJS 7 removed deep imports: rxjs/Observable and rxjs/Subscription → rxjs (this is why rxjs-compat is gone).
• Misc lint-driven fixes: typed the ga global, dropped unused imports/any, let→const, removed empty lifecycle stubs, renamed the item selector → app-item (and its template usage) to satisfy the component-selector prefix rule.

Other

• README.md: removed the dead travis-ci.org build badge; refreshed build/lint/test/e2e instructions and Node 20 requirement. Deleted .travis.yml. Standardized on npm (removed yarn.lock, committed package-lock.json); added .nvmrc (Node 20) and ignored .angular/cache + Playwright artifacts.

Verification

• npm run build ✅ (service worker generated)
• npm run lint ✅ (all files pass)
• npm test ✅ (3/3 specs, ChromeHeadless)

Notes / follow-ups

• Builds emit non-blocking Sass deprecation warnings (@import, darken()); the SCSS theme migration is out of scope here.
• firebase.json hosting.public (dist) already didn't match the build output path before this change; deployment config was left as-is.
• Requires Node 20+ now — the dev environment blueprint should pin Node 20 (proposed separately).

Link to Devin session: https://app.devin.ai/sessions/a0f3b34a7f4b486c9d89067ee0649840
Requested by: @yubin-jee

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