feat: hide performance menu item if disabled (#832)

Hide the Performance UI item of the navigation bar if its disabled.

ui-svelte/src/components/Header.svelte

@@ -3,6 +3,7 @@
   import { screenWidth, toggleTheme, themeMode, appTitle, isNarrow } from "../stores/theme";
   import { currentRoute } from "../stores/route";
   import { playgroundActivity } from "../stores/playgroundActivity";
+  import { performanceEnabled } from "../stores/api";
   import ConnectionStatus from "./ConnectionStatus.svelte";
 
   function handleTitleChange(newTitle: string): void {
@@ -84,16 +85,18 @@
     >
       Logs
     </a>
-    <a
-      href="/performance"
-      use:link
-      class="text-gray-600 hover:text-black dark:text-gray-300 dark:hover:text-gray-100 p-1 whitespace-nowrap"
-      class:font-semibold={isActive("/performance", $currentRoute)}
-      class:underline={isActive("/performance", $currentRoute)}
-      class:underline-offset-4={isActive("/performance", $currentRoute)}
-    >
-      Performance
-    </a>
+    {#if $performanceEnabled}
+      <a
+        href="/performance"
+        use:link
+        class="text-gray-600 hover:text-black dark:text-gray-300 dark:hover:text-gray-100 p-1 whitespace-nowrap"
+        class:font-semibold={isActive("/performance", $currentRoute)}
+        class:underline={isActive("/performance", $currentRoute)}
+        class:underline-offset-4={isActive("/performance", $currentRoute)}
+      >
+        Performance
+      </a>
+    {/if}
     <button onclick={toggleTheme} title="Toggle theme (current: {$themeMode})">
       {#if $themeMode === "system"}
         <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="currentColor" class="w-5 h-5">