Refactors authentication logic

Simplifies authentication checks by using a boolean conversion for the access token.

Ensures that the access token is set to null instead of an empty string when a 401 error is encountered and not explicitly handled, improving consistency.

Author: niemyjski

src/Exceptionless.Web/ClientApp/src/routes/(app)/+layout.svelte

@@ -37,7 +37,7 @@
     }
 
     let { children }: Props = $props();
-    let isAuthenticated = $derived(accessToken.current !== null);
+    let isAuthenticated = $derived(!!accessToken.current);
     const sidebar = useSidebar();
     let isCommandOpen = $state(false);
 

src/Exceptionless.Web/ClientApp/src/routes/+layout.svelte

@@ -42,7 +42,7 @@
         }
 
         if (status === 401 && !ctx.options.expectedStatusCodes?.includes(401)) {
-            accessToken.current = '';
+            accessToken.current = null;
             return;
         }