refactor(docs-infra): automate algolia index name based on package version

Previously, the Algolia index name was hardcoded in the configuration, requiring manual updates for every new major release branch.

This commit automates the index name selection by deriving the version directly @angular/core. It dynamically assigns:
- `angular_next_dev` for pre-releases (`-next`, `-rc`) and local snapshots (`0.0.0`).
- `angular_vXX` (e.g., `angular_v19`) for stable releases.

Author: alessiopelliccione

adev/src/app/environment.ts

@@ -6,16 +6,24 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
+import {VERSION} from '@angular/core';
+const major = VERSION.major;
+
+const isPreRelease =
+  VERSION.full.includes('-next') || VERSION.full.includes('-rc') || VERSION.full === '0.0.0';
+
+// NOTE: Although the index name is determined automatically here, the actual index
+// must be MANUALLY created on the Algolia dashboard for every new major version.
+const indexName = isPreRelease ? 'angular_next_dev' : `angular_v${major}`;
+
 export default {
   production: true,
   // Those values are publicly visible in the search request headers, and presents search-only keys.
   // https://www.algolia.com/doc/guides/security/api-keys/#search-only-api-key
   algolia: {
     appId: 'L1XWT2UJ7F',
     apiKey: 'dfca7ed184db27927a512e5c6668b968',
-    // The indexName value must match the branch it's on.
-    // So it needs to be updated on release of the new major on the patch branch.
-    indexName: 'angular_next_dev',
+    indexName: indexName,
   },
   googleAnalyticsId: 'G-XB6NEVW32B',
 };