chore(uix nav): add Layout group to sidebar for the 8 new primitives

Surfaces Box / Flex / Grid / Stack / Group / Wrap / Container / Section
in the docs sidebar. Pages already existed at `/uix/components/{name}/`
from `9ec2a57a` but weren't navigable from the chrome.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/routes/uix/+layout@.svelte

@@ -196,6 +196,20 @@
 				{ slug: '/uix/components/toast', label: 'Toast' },
 				{ slug: '/uix/components/tooltip', label: 'Tooltip' }
 			]
+		},
+		{
+			kind: 'group',
+			heading: 'Layout',
+			items: [
+				{ slug: '/uix/components/box', label: 'Box' },
+				{ slug: '/uix/components/flex', label: 'Flex' },
+				{ slug: '/uix/components/grid', label: 'Grid' },
+				{ slug: '/uix/components/stack', label: 'Stack' },
+				{ slug: '/uix/components/group', label: 'Group' },
+				{ slug: '/uix/components/wrap', label: 'Wrap' },
+				{ slug: '/uix/components/container', label: 'Container' },
+				{ slug: '/uix/components/section', label: 'Section' }
+			]
 		}
 	];