[nan-661] use public server url (NangoHQ#1932)

## Describe your changes
Use public server url variable instead of faulty replacement logic

## Issue ticket number and link
NAN-661

## Checklist before requesting a review (skip if just adding/editing
APIs & templates)
- [ ] I added tests, otherwise the reason is: 
- [ ] I added observability, otherwise the reason is:
- [ ] I added analytics, otherwise the reason is:

packages/server/lib/controllers/auth.controller.ts

@@ -380,7 +380,7 @@ class AuthController {
                 clientId: process.env['WORKOS_CLIENT_ID'] || '',
                 provider,
                 redirectUri: `${basePublicUrl}/api/v1/login/callback`,
-                state: JSON.stringify(inviteParams)
+                state: Buffer.from(JSON.stringify(inviteParams)).toString('base64')
             });
 
             res.send({ url: oAuthUrl });

packages/utils/lib/environment/detection.ts

@@ -1,7 +1,7 @@
 import { NodeEnv, localhostUrl } from './constants.js';
 
 export const baseUrl = process.env['NANGO_SERVER_URL'] || localhostUrl;
-export const basePublicUrl = process.env['NANGO_SERVER_URL'] ? process.env['NANGO_SERVER_URL'].replace('api.', 'app.') : baseUrl;
+export const basePublicUrl = process.env['NANGO_PUBLIC_SERVER_URL'] || baseUrl;
 
 export const isStaging = process.env['NODE_ENV'] === NodeEnv.Staging;
 export const isProd = process.env['NODE_ENV'] === NodeEnv.Prod;