Slack integration link is broken

Clicking `Settings` -> `Slack` -> `Manage in PostHog Web` routes to a broken URL

<img width="3332" height="1634" alt="Image" src="https://github.com/user-attachments/assets/ef68b162-5d73-4198-9676-fd25aac23b07" />

<img width="3606" height="2070" alt="Image" src="https://github.com/user-attachments/assets/107cfda5-b363-48cd-96cf-881018a682b1" />