angularfire chore(workspace): update sample app to Angular 20

Issue number for this PR: #3669 (required)
Docs included?: no significant changes
Test units included?: yes, and they pass now 🤓
In a clean directory, yarn install, yarn test run successfully? yes, for the sample directory

Updating sample app to Angular 20

installing angular/fire v20 was fun, I had to initially uninstall it from the sample app, update to Angular 20, then build v20 from source, then add it back in
many of the changes are lint-related
Karma tests are passing with the inclusion of a test.ts file -- it kept complaining about needing Zone.js even though this is a zoneless app, since there's only 3 tests, we may want to explore Vitest as an alternative
sadly, I did need to pass --no-verify when committing this, there are ~350 lint errors in the repo and I didn't want to include those fixes in this change
both client and server apps run, no errors appear locally, and most functionality that I could test continues to work
many, many updates needed to this app to bring it in line with newer patterns in Angular that have evolved since Signals came out, but we can tackle those in future PRs

Sep 10 '25 01:09 markgoho

@jamesdaniels any feedback for this PR?

Sep 25 '25 02:09 markgoho

@jamesdaniels should we try to get this in before v21 comes along? 🤓

Nov 01 '25 14:11 markgoho