Upgrade Angular & Packages, Big Clean up

[dills122]

Summary

• upgrade the Angular frontend through Angular 20 and stabilize the app after each major hop
• replace Bootstrap with Tailwind utilities while keeping Nebular in place
• clean up backend/shared dependency drift and modernize Rush/pnpm repo tooling

What Changed

• upgraded apps/chat-frontend from Angular 16 to Angular 20, including Nebular, ngx-socket-io, lint/test/build config, and environment-driven socket config
• removed Bootstrap, added Tailwind utility support, and tightened layout/spacing on the main app shell, home page, and create-session flow
• removed stale frontend Protractor/e2e scaffolding and refreshed frontend/root docs to match the current stack
• cleaned backend/shared package manifests, aligned socket.io and shared TypeScript/ESLint versions, and removed unused/stale backend dependencies
• upgraded Rush to 5.169.3, pnpm to 10.31.0, refreshed generated Rush helper scripts, regenerated workspace/autoinstaller lockfiles, and updated GitHub Actions to checkout@v4 and setup-node@v4
• aligned @typescript-eslint to 8.56.1 across packages and fixed a backend lint issue in apps/chat-backend/src/shared/util.ts

Validation

• npm run build in apps/chat-frontend
• npm run lint in apps/chat-frontend
• npm run build in apps/chat-backend
• npm test -- --runInBand in apps/chat-backend
• node common/scripts/install-run-rush.js build
• node common/scripts/install-run-rush.js lint

Scope Notes

• frontend Karma/browser tests were not revalidated in the sandbox because of the known port-binding limitation
• rush build still reports the existing Angular CommonJS optimization warning from socket.io-parser
• Rush still warns about a phantom /Users/dsteele/repos/node_modules folder outside this repo; that was not changed here