feat(client): improve type safety in environment

apps/client/src/environments/environment.prod.ts

@@ -1,4 +1,6 @@
-export const environment = {
+import type { GfEnvironment } from '@ghostfolio/ui/tokens';
+
+export const environment: GfEnvironment = {
   lastPublish: '{BUILD_TIMESTAMP}',
   production: true,
   stripePublicKey: ''

apps/client/src/environments/environment.ts

@@ -1,8 +1,9 @@
 // This file can be replaced during build by using the `fileReplacements` array.
 // `ng build --prod` replaces `environment.ts` with `environment.prod.ts`.
 // The list of file replacements can be found in `angular.json`.
+import type { GfEnvironment } from '@ghostfolio/ui/tokens';
 
-export const environment = {
+export const environment: GfEnvironment = {
   lastPublish: null,
   production: false,
   stripePublicKey: ''