Update fetch call to check API reachability

the original version of this code calls "https://jellyfin.domain.tld". this works for most people. some people however don't have a properly set up reverse proxy. by adding a forward slash, we remove the issue for users who have reverse proxies that don't redirect from   "https://jellyfin.domain.tld" to "https://jellyfin.domain.tld/"

providers/NetworkStatusProvider.tsx

@@ -24,7 +24,7 @@ const NetworkStatusContext = createContext<NetworkStatusContextType | null>(
 async function checkApiReachable(basePath?: string): Promise<boolean> {
   if (!basePath) return false;
   try {
-    const response = await fetch(basePath, { method: "HEAD" });
+    const response = await fetch(basePath + "/", { method: "HEAD" });
     return response.ok;
   } catch {
     return false;