Update admin app authentication in API mode too, reusing components between it and the main app.

frontend/src/components/AuthRequiredMessage.vue

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+<template>
+  <div class="message-container">
+    <div class="message-content">
+      <h2>🔒 Authentication Required</h2>
+      <p>{{ message }}</p>
+      <div class="button-row">
+        <button class="btn-primary" @click="$emit('reload')">Reload Page</button>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup>
+defineProps({
+  message: {
+    type: String,
+    default: 'You need to authenticate to access this page.'
+  }
+})
+
+defineEmits(['reload'])
+</script>
+
+<style scoped>
+.message-container {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  height: 100vh;
+  padding: 2rem;
+}
+
+.message-content {
+  text-align: center;
+  max-width: 480px;
+}
+
+.message-content h2 {
+  margin: 0 0 1rem;
+  color: var(--color-heading);
+}
+
+.message-content p {
+  color: var(--color-text-muted);
+  margin: 0 0 1.5rem;
+}
+
+.message-content .button-row {
+  display: flex;
+  gap: 0.75rem;
+  justify-content: center;
+}
+</style>

frontend/src/components/LoadingView.vue

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+<template>
+  <div class="loading-container">
+    <div class="loading-spinner"></div>
+    <p>{{ message }}</p>
+  </div>
+</template>
+
+<script setup>
+defineProps({
+  message: {
+    type: String,
+    default: 'Loading...'
+  }
+})
+</script>
+
+<style scoped>
+.loading-container {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  height: 100vh;
+  gap: 1rem;
+}
+
+.loading-spinner {
+  width: 40px;
+  height: 40px;
+  border: 4px solid var(--color-border);
+  border-top: 4px solid var(--color-primary);
+  border-radius: 50%;
+  animation: spin 1s linear infinite;
+}
+
+@keyframes spin {
+  0% { transform: rotate(0deg); }
+  100% { transform: rotate(360deg); }
+}
+
+.loading-container p {
+  color: var(--color-text-muted);
+  margin: 0;
+}
+</style>