fix: Use svelte:component for dynamic icon rendering in ThemeToggle

Replace invalid {@const} usage with proper <svelte:component this={...}> syntax.
The {@const} tag must be an immediate child of specific block structures,
not directly inside regular HTML elements.

src/lib/components/layout/ThemeToggle.svelte

@@ -51,18 +51,16 @@
 <!-- Theme Toggle Dropdown -->
 <div class="dropdown dropdown-end">
 	<button tabindex="0" class="btn btn-ghost btn-circle" aria-label="Theme">
-		{@const IconComponent = currentIcon}
-		<IconComponent class="h-5 w-5" />
+		<svelte:component this={currentIcon} class="h-5 w-5" />
 	</button>
 	<ul class="menu dropdown-content z-[1] mt-3 w-52 rounded-box bg-base-100 p-2 shadow-lg">
 		{#each themes as { value, label, icon }}
-			{@const IconComponent = icon}
 			<li>
 				<button
 					class:active={$preferences.theme === value}
 					onclick={() => handleThemeChange(value)}
 				>
-					<IconComponent class="h-4 w-4" />
+					<svelte:component this={icon} class="h-4 w-4" />
 					{label}
 					{#if value === 'auto'}
 						<span class="text-xs text-base-content/60">(System)</span>