chore: bump version to 21.0.0-rc.1 (#3751)

The publish job reads this literal at tag time. The sample's file:
tarball dependency path and its README install example carry the
same version, so they move together.

The root lockfile records the same version in its two version fields.
The sample's lockfile deliberately keeps the rc.0 tarball name, because
it also records that tarball's integrity hash.

Author: armando-navarro

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@angular/fire",
-  "version": "21.0.0-rc.0",
+  "version": "21.0.0-rc.1",
   "description": "Angular + Firebase = ❤️",
   "publishConfig": {
     "registry": "https://wombat-dressing-room.appspot.com",

package.json

@@ -4,7 +4,7 @@ This project was generated using [Angular CLI](https://github.com/angular/angula
 
 ## AngularFire tarball
 
-The sample consumes the library as `file:../angular-fire-21.0.0-rc.0.tgz`. Produce that file from the repository root before installing here:
+The sample consumes the library as `file:../angular-fire-21.0.0-rc.1.tgz`. Produce that file from the repository root before installing here:
 
 ```bash
 npm ci
@@ -16,7 +16,7 @@ The root build ends with `npm pack ./dist/packages-dist`, which writes `angular-
 Then, from this `sample/` folder, install the dependencies by naming the tarball explicitly:
 
 ```bash
-npm install ../angular-fire-21.0.0-rc.0.tgz
+npm install ../angular-fire-21.0.0-rc.1.tgz
 ```
 
 A plain `npm install` is not reliable here. `package-lock.json` records the integrity hash of the tarball built by whoever committed the lockfile, and a tarball you build yourself can hash differently. With a cold npm cache the install then fails with an `EINTEGRITY` error. With a warm cache that holds the recorded hash, npm installs the stale cached copy and exits successfully, so you would be testing a library you did not build. Naming the tarball installs the file on disk and rewrites the recorded hash in your local `package-lock.json`. Leave that lockfile change uncommitted.

sample/README.md

@@ -14,7 +14,7 @@
     "@angular/common": "^21.0.0",
     "@angular/compiler": "^21.0.0",
     "@angular/core": "^21.0.0",
-    "@angular/fire": "file:../angular-fire-21.0.0-rc.0.tgz",
+    "@angular/fire": "file:../angular-fire-21.0.0-rc.1.tgz",
     "@angular/forms": "^21.0.0",
     "@angular/platform-browser": "^21.0.0",
     "@angular/platform-server": "^21.0.0",