feat(frontend): darken neutral theme and reorder theme switcher

- make neutral theme a warm dark graphite
- order switches as dark -> neutral -> light -> system
- replace neutral icon with contrast glyph

frontend/src/lib/components/ThemeSwitcher.svelte

@@ -4,9 +4,9 @@
 	import { theme, type Theme } from '$lib/stores/theme.svelte';
 
 	const options: { value: Theme; label: string; icon: IconName }[] = [
-		{ value: 'light', label: 'Light', icon: 'light_mode' },
 		{ value: 'dark', label: 'Dark', icon: 'dark_mode' },
-		{ value: 'neutral', label: 'Neutral', icon: 'palette' },
+		{ value: 'neutral', label: 'Neutral', icon: 'contrast' },
+		{ value: 'light', label: 'Light', icon: 'light_mode' },
 		{ value: 'system', label: 'System', icon: 'brightness_auto' }
 	];
 </script>

frontend/src/lib/icons/registry.ts

@@ -45,7 +45,8 @@ export const icons = {
 	grid_view: { path: '<path fill="currentColor" d="M3 3v8h8V3zm10 0v8h8V3zM3 13v8h8v-8zm10 0v8h8v-8z"/>' },
 	wallpaper: { path: '<path fill="currentColor" d="M4 4h7V2H4c-1.1 0-2 .9-2 2v7h2zm6 9l-4 5h12l-3-4l-2.03 2.71zm7-4.5c0-.83-.67-1.5-1.5-1.5S14 7.67 14 8.5s.67 1.5 1.5 1.5S17 9.33 17 8.5M20 2h-7v2h7v7h2V4c0-1.1-.9-2-2-2m0 18h-7v2h7c1.1 0 2-.9 2-2v-7h-2zM4 13H2v7c0 1.1.9 2 2 2h7v-2H4z"/>' },
 	fullscreen: { path: '<path fill="currentColor" d="M7 14H5v5h5v-2H7zm-2-4h2V7h3V5H5zm12 7h-3v2h5v-5h-2zM14 5v2h3v3h2V5z"/>' },
-	fullscreen_exit: { path: '<path fill="currentColor" d="M5 16h3v3h2v-5H5zm3-8H5v2h5V5H8zm6 11h2v-3h3v-2h-5zm2-11v3h-2v2h5V5z"/>' }
+	fullscreen_exit: { path: '<path fill="currentColor" d="M5 16h3v3h2v-5H5zm3-8H5v2h5V5H8zm6 11h2v-3h3v-2h-5zm2-11v3h-2v2h5V5z"/>' },
+	contrast: { path: '<path fill="currentColor" fill-rule="evenodd" d="M12 2a10 10 0 1 0 0 20 10 10 0 0 0 0-20zM12 4a8 8 0 1 0 0 16 8 8 0 0 0 0-16zM12 4a8 8 0 0 1 0 16z"/>' }
 } satisfies Record<string, IconDef>;
 
 export type IconName = keyof typeof icons;