Refactor: Isolate API key storage

src/core/storage.js

@@ -0,0 +1,13 @@
+export const STORAGE_KEY = 'vibegif_api_key';
+
+export function getApiKey() {
+  return localStorage.getItem(STORAGE_KEY) || '';
+}
+
+export function setApiKey(key) {
+  localStorage.setItem(STORAGE_KEY, (key || '').trim());
+}
+
+export function hasApiKey() {
+  return !!getApiKey();
+}