[UX] Add custom models to new Duo page (Unified Settings)

Overview

This issue is awaiting finalization/blocked by the completion of the Unified AI Settings page. When that is implemented, then we will move self-hosted models into that page.

We need to add functionality for Custom Models in the Admin section of the GitLab Duo settings page for Self-Managed instances. This feature will allow administrators to manage and configure custom AI models for use with GitLab Duo.

Initial WIP Proposals

Proposal	Pros	Cons
Option 1 — Place the Self-hosted and feature-to-model configuration interactions on the GitLab Duo page	All information is immediately visible on one page. Easier navigation for users who prefer a single-page view Reduces the number of clicks needed to access all settings	The page has a higher potential to become quite dense, with a lot of information and configuration options. Potential performance issues if tables are large It is harder to interconnect other Custom Model workflows like Logs, validation, model routing, etc.
Option 2 — Create jump-off cards to dedicated pages for the Self-hosted models page and feature-to-model configuration page	Cleaner main settings page with better organisation More breathing space for detailed information on dedicated pages It is easier to scale and add new features without cluttering the main page	It would most likely require additional navigation Slightly higher development effort to create and maintain multiple pages Potential for Admins to miss information

Recommended proposal

📁 Figma project

Self-hosted models	Self-hosted models + Audit logs	Self-hosted models + Audit logs + Model validation
We add an additional card section on the Gitlab duo page.	When available in a future release, we incorporate Audit Logs as an additional card on the page.	When available in a future release, we incorporate Model validation as an additional card on the page.
This then leads the user to the GitLab Duo self-hosted page that will be nested underneath the parent GitLab Duo page.	This also leads the user to the Audit logs view, a standalone page nested underneath the parent GitLab Duo page.	This would also lead the user to the Model validation view, a standalone page nested underneath the parent GitLab Duo page.