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/AppForm.svelte

@@ -4,6 +4,8 @@
 	import type { z } from 'zod';
 	import type { createAppSchema } from '$lib/utils/validators.js';
 	import AppIconPicker from './AppIconPicker.svelte';
+	import IconGrid from '$lib/components/ui/IconGrid.svelte';
+	import type { IconGridItem } from '$lib/components/ui/IconGrid.svelte';
 
 	type AppSchema = z.infer<typeof createAppSchema>;
 
@@ -19,6 +21,11 @@
 	});
 
 	let showAdvanced = $state(false);
+
+	const healthcheckMethodItems: IconGridItem[] = [
+		{ value: 'GET', icon: '🔍', label: 'GET', desc: 'Full response' },
+		{ value: 'HEAD', icon: '📋', label: 'HEAD', desc: 'Headers only' }
+	];
 </script>
 
 <form method="POST" {action} use:enhance class="space-y-4">
@@ -140,20 +147,17 @@
 				<div class="grid grid-cols-1 gap-4 sm:grid-cols-3">
 					<div>
 						<label
-							for="healthcheckMethod"
 							class="mb-1 block text-sm font-medium text-card-foreground"
 						>
 							{$t('app.healthcheck_method')}
 						</label>
-						<select
-							id="healthcheckMethod"
+						<IconGrid
+							items={healthcheckMethodItems}
+							value={$form.healthcheckMethod ?? 'GET'}
+							onchange={(v) => ($form.healthcheckMethod = v as 'GET' | 'HEAD')}
 							name="healthcheckMethod"
-							bind:value={$form.healthcheckMethod}
-							class="w-full 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="GET">GET</option>
-							<option value="HEAD">HEAD</option>
-						</select>
+							columns={2}
+						/>
 					</div>
 
 					<div>