Improve admin navigation and local API reachability

frontend/src/lib/api.ts

@@ -15,7 +15,7 @@ import type {
   WinnerArchiveResponse,
 } from '../types/awards'
 
-const API_URL = import.meta.env.VITE_API_URL ?? 'http://localhost:5084'
+const API_URL = import.meta.env.VITE_API_URL ?? 'http://127.0.0.1:5084'
 const AUTH_TOKEN_KEY = 'vtsa-session-token'
 
 function getAuthToken() {
@@ -31,6 +31,8 @@ async function getJson<T>(path: string): Promise<T> {
           Authorization: `Bearer ${token}`,
         }
       : undefined,
+  }).catch(() => {
+    throw new Error(`API nicht erreichbar (${API_URL}). Bitte Backend starten.`)
   })
   if (!response.ok) {
     throw new Error(`API request failed for ${path}`)
@@ -47,6 +49,8 @@ async function sendJson<TResponse>(path: string, method: 'POST' | 'PUT', body: u
       ...(token ? { Authorization: `Bearer ${token}` } : {}),
     },
     body: JSON.stringify(body),
+  }).catch(() => {
+    throw new Error(`API nicht erreichbar (${API_URL}). Bitte Backend starten.`)
   })
 
   if (!response.ok) {