fix(site): only highlight Providers item on exact match in AI settings sidebar (#25700)

## Problem

When visiting `/ai/settings/governance`, both **AI Governance** and
**Providers** items in the AI settings subnav appear highlighted as
active.

## Cause

`SettingsSidebarNavItem` is built on react-router's `<NavLink>`, which
by default treats a link as active when the current URL **starts with**
the link's `to` path. Since `/ai/settings/governance` starts with
`/ai/settings`, the Providers item is also marked active.

## Fix

Pass `end` on the Providers nav item so it only matches when the path is
exactly `/ai/settings` (the index route). The `SettingsSidebarNavItem`
component already supports this prop for exactly this case.

Co-authored-by: blink-so[bot] <211532188+blink-so[bot]@users.noreply.github.com>

site/src/modules/management/AISettingsSidebarView.tsx

@@ -22,7 +22,9 @@ const AISettingsSidebarView: FC<AISettingsSidebarViewProps> = ({
 						AI Governance
 					</SidebarNavItem>
 				)}
-				<SidebarNavItem href="/ai/settings">Providers</SidebarNavItem>
+				<SidebarNavItem href="/ai/settings" end>
+					Providers
+				</SidebarNavItem>
 				{permissions.editDeploymentConfig && (
 					<SidebarNavItem href="/agents/settings/agents">
 						<div className="flex flex-row items-center gap-1">