chore(sample): update the sample app to Angular 21 - #3671

Continues the Angular 19 to 20 update in this PR up to Angular 21, so the
sample matches the workspace library (which is on Angular 21).

- bump all @angular/* to ^21.0.0 and @angular/fire to the Angular 21 build;
  drop the unused, deprecated @angular/animations and the deprecated
  @angular/platform-browser-dynamic; bump @types/node to ^22 for the Node 22
  runtime.
- main.server.ts: pass the BootstrapContext that Angular 21 requires for the
  server bootstrap. Without it, build-time route extraction fails with NG0401.
- test.ts: reconcile the test setup with the app's zoneless mode. Drop the
  zone.js imports, switch to @angular/platform-browser/testing, and provide
  zoneless change detection so fixture.detectChanges works.
- rename the project ng20-test to ng21-test throughout: package.json name and
  serve:ssr script, angular.json project key/outputPath/buildTargets, the
  index.html and README titles, and AppComponent.title with its spec.

Builds and unit tests pass against the Angular 21 library.

… the tarball

Delete the hand-rolled src/test.ts. When the test target in
angular.json does not name an entry file, the @angular/build:karma
builder generates the test-environment initialization itself. The
Firebase test providers already lived in the spec, so the diff moves
only the zoneless change-detection provider there.

firebase-tools moves into devDependencies so npm start stops
downloading the newest release on every run and cannot drift ahead of
the firebase-tools versions the library supports. The start script
runs the firebase command that install provides.

The README now documents how to produce the tarball the sample
installs the library from.

Angular 21 generates new applications with the @angular/build:unit-test
builder running vitest, so the sample now matches what the CLI produces
for its target version. The bare builder entry picks up the same
defaults a new app gets.

The specs run unchanged: describe, it, and expect keep working as
vitest globals, so only the type declarations move from jasmine to
vitest/globals.

The karma and jasmine packages leave devDependencies, replaced by
vitest, jsdom (the browserless DOM the tests now run in), and
@vitest/coverage-v8 so ng test --coverage keeps producing reports.

The sample imports from firebase/auth directly but never declared the
package, relying on the copy @angular/fire bundles being hoisted where
the import can find it. An application that sets up @angular/fire
through ng add carries its own firebase entry, so the sample now
matches, and npm dedupes the two ranges to a single installed copy.

Angular 21 scaffolds its SSR server on express ^5.1.0, so the sample
now matches, with @types/express moving to the matching major.

Express 5 changed route-pattern parsing, so the catch-all handler is
registered without the '/**' path string, the same shape the v21
scaffold uses. The two-step dirname/fileURLToPath computation becomes
import.meta.dirname, available on every Node version Angular 21
supports.

The listener block also adopts the scaffold's shape: the server now
starts under the PM2 process manager too, and the listen callback
throws startup errors instead of ignoring them.

The root tsconfig becomes the solution-style coordinator the v21 CLI
generates: it compiles nothing itself and references the app and spec
configs as separate projects, which gives editors the right typing
per context.

The module setting moves to preserve, which implies the bundler
resolution and import interop the older explicit flags provided, and
the unused outDir goes away. tsconfig.app.json switches from listing
entry files by hand to including all sources except specs.

…context

Calls like signInAnonymously and updateDoc were made directly inside
click handlers, which run after the component's injection context is
gone, so AngularFire logged its outside-injection-context warning and
could not apply its change-detection and SSR safeguards there.

The two affected components, auth and upboats, now capture an
EnvironmentInjector and re-enter it with runInInjectionContext inside
each handler, the exact pattern docs/zones.md teaches. The functions
demo needs no wrap, because its callable is produced once during field
initialization, inside the injection context, and the returned function
never touches the injector. The raw Firebase SDK call, signInWithPopup,
is outside the warning system's scope and stays as is.

The functions folder is its own small project, and without its own
install and build the functions emulator skips it with a warning, so
the Call! demo had no backend. The README now documents the one-time
setup.

Its engines entry moves from Node 20 to 22, matching the runtime the
deploy schematic generates, and its TypeScript compile target moves to
es2022 alongside.

The heading was the PascalCased project name the CLI scaffold derived
from the folder, never a chosen title.

Nothing imports it: not the sample source and not the shipped
@angular/fire code. It also sat in the build's externalDependencies
list, which only matters for packages that actually appear in imports.
It looks left over from an earlier approach to the session cookie
handling that the current server-side code no longer uses.

angular.json drops the extract-i18n target, outputPath, and index,
none of which ng new generates anymore (the removed values equal the
builder's defaults), and gains the security.allowedHosts entry new
apps carry.

@types/node moves from ^22 to ^20.17.19, the range new apps declare.
The types package should describe the OLDEST Node the app supports,
which is Angular 21's 20.19 requirement, so the compiler rejects APIs
that would crash there. Every API the server uses is typed well within
that range.

The development-server section told readers to run bare ng serve, but
every demo talks to the local emulators, so that yields a page with no
backend. It now leads with npm start, which boots the seeded emulators
and then serves.

The scaffold's end-to-end section instructed ng e2e, which errors
because no e2e target is configured, so it goes until a real e2e setup
exists.

The sample app declares firebase and @angular/fire bundles its own
firebase dependency. npm installs a single shared copy only while the
two version ranges overlap. If they ever stop overlapping, npm installs
two copies side by side and objects from one copy are rejected by the
other at runtime. This assertion fails loudly the moment that happens.

The bare unit-test target runs vitest in jsdom, so nothing writes
__screenshots__/ and the entry's browser-mode comment was wrong.