refactor(domain-manager): simplify frontend URL configuration (#10194)

Replaced multiple environment variables for frontend URL construction
with a single FRONTEND_URL variable. This change reduces complexity and
improves clarity by consolidating frontend URL handling into one source.
Updated relevant validations and removed unused variables like
FRONT_PROTOCOL and FRONT_PORT.

Fix #10016

packages/twenty-website/src/content/developers/self-hosting/setup.mdx

@@ -155,8 +155,7 @@ yarn command:prod cron:calendar:ongoing-stale
     ['FRONT_DOMAIN', 'localhost', 'Domain of the hosted frontend'],
     ['DEFAULT_SUBDOMAIN', 'app', 'The default subdomain name when multiworkspace mode is enabled'],
     ['SERVER_URL', 'http://localhost:3000', 'Url to the hosted server'],
-    ['FRONT_PROTOCOL', 'http', 'protocol of the frontend server. Could be `http` or `https`'],
-    ['FRONT_PORT', '3001', 'Port of the frontend server.'],
+    ['FRONTEND_URL', '$SERVER_URL', 'Url to the frontend server. Same as SERVER_URL by default'],
     ['PORT', '3000', 'Port of the backend server'],
     ['CACHE_STORAGE_TTL', '3600 * 24 * 7', 'Cache TTL in seconds']
     ]}></ArticleTable>