fix(core): drop the unused optional @angular/platform-server peer (#3792)

npm 10, and npm 11 before 11.20, resolve a missing optional peer anyway
while installing. For an app whose package.json uses caret ranges and
whose Angular is one patch behind the newest, npm picks the newest
@angular/platform-server, which requires that exact newest
@angular/core, and the install stops with ERESOLVE. Every current Node
line bundles one of those npm versions.

Nothing in the published package imports @angular/platform-server, so
the peer is removed. Apps that render on the server still install it
themselves, as they already do.

Author: armando-navarro

src/package.json

@@ -31,14 +31,12 @@
     "@angular/common": "^21.2.0",
     "@angular/core": "^21.2.0",
     "@angular/platform-browser": "^21.2.0",
-    "@angular/platform-server": "^21.2.0",
     "rxjs": "~7.8.0",
     "firebase-tools": "^14.0.0 || ^15.0.0",
     "typescript": ">=5.8 <6.0"
   },
   "peerDependenciesMeta": {
     "firebase-tools": { "optional": true },
-    "@angular/platform-server": { "optional": true },
     "typescript": { "optional": true }
   },
   "dependencies": {