…#3813)

The docs on 21.0.x still install with @angular/fire@next, call 21 a
release candidate, and carry the AI-agent note for the firebase-tools
15.26 crash that #3769 fixed on this branch. The 21.0.0 tag is cut from
this branch, so its docs should describe the release.

The upgrade command keeps @angular/fire unversioned: only the first
@angular/ package in an ng update command picks the CLI that runs it.
The Node.js note gives the versioned form for updating AngularFire alone.

Add @angular/fire/firestore/pipelines and
@angular/fire/firestore/lite/pipelines, generated from firebase's
pipelines entry points, plus a pipeline() declaration on Lite's
Firestore that firebase's own Lite typings leave out.

Fixes #3693
Refs #3755

(cherry picked from commit 80ed66b)

tools/build.ts copied the whole docs/ tree into the publish output,
so every release carried 53 Markdown and image files, about 1 MB
unpacked and 42 percent of the compressed tarball, that nothing in
the package reads. The copy dates from the 6.0.0 build script
(#2282).

Shipped docs freeze at the installed version while the GitHub copies
move on, and docs/firebase.json inside node_modules has been mistaken
for a config file to point a deploy at. README.md still ships.

Measured on the 22.0.0 build at f95d598: 175 to 122 files, 4,694,110
to 3,663,246 bytes unpacked, 2,021,273 to 1,173,999 bytes compressed.

(cherry picked from commit 0c924da)

…te (#3817)

The auth guide's cookie sync and the sample app imported
beforeAuthStateChanged from firebase/auth, because AngularFire's version
kept the app unstable until the first sign-in or sign-out (#3748). The
fix (#3770) shipped in 20.1.1 and 21.0.0-rc.2, so both now import it
from @angular/fire/auth, and the guide's note lists the releases that
still need the workaround.

The v21 upgrade guide covered only getImagenModel. firebase 12.18
removed every Imagen export, and the migration warns about
getImagenModel only in files that imported an old Vertex AI entry point.

Fixes #3815
Fixes #3816

(cherry picked from commit 503ce83)