docs(uix): add Toggle group · Alert dialog · Dropdown menu to sidebar nav

Wires the three Tier 1 sprint components into the IA:
- 'Toggle group' under Controls (next to Toggle)
- 'Alert dialog' under Overlays (next to Dialog)
- 'Dropdown menu' under Overlays (next to Popover)

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

web/routes/uix/+layout@.svelte

@@ -125,6 +125,7 @@
 			heading: 'Controls',
 			items: [
 				{ slug: '/uix/components/toggle', label: 'Toggle' },
+				{ slug: '/uix/components/toggle-group', label: 'Toggle group' },
 				{ slug: '/uix/components/switch', label: 'Switch' },
 				{ slug: '/uix/components/checkbox', label: 'Checkbox' },
 				{ slug: '/uix/components/radio-group', label: 'Radio group' },
@@ -193,8 +194,10 @@
 			heading: 'Overlays',
 			items: [
 				{ slug: '/uix/components/dialog', label: 'Dialog' },
+				{ slug: '/uix/components/alert-dialog', label: 'Alert dialog' },
 				{ slug: '/uix/components/drawer', label: 'Drawer' },
 				{ slug: '/uix/components/popover', label: 'Popover' },
+				{ slug: '/uix/components/dropdown-menu', label: 'Dropdown menu' },
 				{ slug: '/uix/components/toast', label: 'Toast' },
 				{ slug: '/uix/components/tooltip', label: 'Tooltip' }
 			]