feat(src): remove /playground route

* The functionality is not used
* Remove unused code

Refs: PRODAI-198

Author: thlehmann-ionos

src/lib/components/layout/Sidebar/UserMenu.svelte

@@ -76,36 +76,6 @@
 			{/if}
 
 			{#if role === 'admin'}
-				<a
-					class="flex rounded-md py-2 px-3 w-full hover:bg-gray-50 dark:hover:bg-gray-800 transition"
-					href="/playground"
-					on:click={() => {
-						show = false;
-
-						if ($mobile) {
-							showSidebar.set(false);
-						}
-					}}
-				>
-					<div class=" self-center mr-3">
-						<svg
-							xmlns="http://www.w3.org/2000/svg"
-							fill="none"
-							viewBox="0 0 24 24"
-							stroke-width="1.5"
-							stroke="currentColor"
-							class="size-5"
-						>
-							<path
-								stroke-linecap="round"
-								stroke-linejoin="round"
-								d="M14.25 9.75 16.5 12l-2.25 2.25m-4.5 0L7.5 12l2.25-2.25M6 20.25h12A2.25 2.25 0 0 0 20.25 18V6A2.25 2.25 0 0 0 18 3.75H6A2.25 2.25 0 0 0 3.75 6v12A2.25 2.25 0 0 0 6 20.25Z"
-							/>
-						</svg>
-					</div>
-					<div class=" self-center truncate">{$i18n.t('Playground')}</div>
-				</a>
-
 				<a
 					class="flex rounded-md py-2 px-3 w-full hover:bg-gray-50 dark:hover:bg-gray-800 transition"
 					href="/admin"