added shortener url env

frontend/.env.example

@@ -1,3 +1,4 @@
 PROTOCOL_HEADER=x-forwarded-proto 
 HOST_HEADER=x-forwarded-host
 DATABASE_URL=postgres://postgres:password@127.0.0.1:5432/link-shortener
+PUBLIC_SHORTENER_URL=http://localhost:3000

frontend/src/routes/(app)/+layout.server.ts

@@ -1,10 +1,11 @@
 import type { LayoutServerLoad } from './$types'
+import { PUBLIC_SHORTENER_URL } from '$env/static/public'
 
 export const load = (async (event) => {
 	const user = event.locals.userObject
 
 	return {
-		shortener_url: process.env.SHORTENER_URL ?? 's.tzgyn.com',
+		shortener_url: PUBLIC_SHORTENER_URL,
 		user: user,
 	}
 }) satisfies LayoutServerLoad