feat: add IconGrid, EntityPicker controls and enhance search panel

Port icon grid and entity picker patterns from wled-screen-controller.
IconGrid replaces plain <select> elements with visual icon grids for
known item sets (widget type, icon type, healthcheck method, permission
level). EntityPicker replaces search dropdowns with a command-palette
style overlay with keyboard navigation and filtering.

Enhance SearchDialog with keyboard navigation (arrow keys, Enter,
Escape), grouped results with section headers, active highlight,
and a footer with shortcut hints.

src/lib/components/app/AppIconPicker.svelte

@@ -1,5 +1,7 @@
 <script lang="ts">
 	import { t } from 'svelte-i18n';
+	import IconGrid from '$lib/components/ui/IconGrid.svelte';
+	import type { IconGridItem } from '$lib/components/ui/IconGrid.svelte';
 
 	interface Props {
 		iconType: string;
@@ -9,9 +11,15 @@
 
 	let { iconType = $bindable('lucide'), iconValue = $bindable(''), onchange }: Props = $props();
 
-	function handleTypeChange(e: Event) {
-		const target = e.target as HTMLSelectElement;
-		iconType = target.value;
+	const iconTypeItems: IconGridItem[] = [
+		{ value: 'lucide', icon: '◇', label: $t('app.icon_lucide') ?? 'Lucide' },
+		{ value: 'simple', icon: '◆', label: $t('app.icon_simple') ?? 'Simple Icons' },
+		{ value: 'url', icon: '🔗', label: $t('app.icon_url') ?? 'Image URL' },
+		{ value: 'emoji', icon: '😀', label: $t('app.icon_emoji') ?? 'Emoji' }
+	];
+
+	function handleTypeChange(value: string) {
+		iconType = value;
 		iconValue = '';
 		onchange?.(iconType, iconValue);
 	}
@@ -27,16 +35,14 @@
 	<label class="block text-sm font-medium text-card-foreground">{$t('app.icon')}</label>
 
 	<div class="flex gap-2">
-		<select
-			value={iconType}
-			onchange={handleTypeChange}
-			class="rounded-md border border-input bg-background px-3 py-2 text-sm text-foreground focus:outline-none focus:ring-2 focus:ring-ring"
-		>
-			<option value="lucide">{$t('app.icon_lucide')}</option>
-			<option value="simple">{$t('app.icon_simple')}</option>
-			<option value="url">{$t('app.icon_url')}</option>
-			<option value="emoji">{$t('app.icon_emoji')}</option>
-		</select>
+		<div class="w-44 shrink-0">
+			<IconGrid
+				items={iconTypeItems}
+				value={iconType}
+				onchange={handleTypeChange}
+				columns={2}
+			/>
+		</div>
 
 		<input
 			type="text"