feat: Expo scaffold + auth screens + core screens (#39-#46, #48)

components/LoadingSpinner.tsx

@@ -0,0 +1,34 @@
+import React from 'react';
+import { View, ActivityIndicator, Text } from 'react-native';
+
+interface LoadingSpinnerProps {
+  message?: string;
+  fullScreen?: boolean;
+  size?: 'small' | 'large';
+}
+
+export const LoadingSpinner: React.FC<LoadingSpinnerProps> = ({
+  message,
+  fullScreen = false,
+  size = 'large',
+}) => {
+  if (fullScreen) {
+    return (
+      <View className="flex-1 items-center justify-center bg-gray-50">
+        <ActivityIndicator size={size} color="#2563EB" />
+        {message && (
+          <Text className="mt-3 text-gray-500 text-sm">{message}</Text>
+        )}
+      </View>
+    );
+  }
+
+  return (
+    <View className="items-center justify-center py-8">
+      <ActivityIndicator size={size} color="#2563EB" />
+      {message && (
+        <Text className="mt-2 text-gray-500 text-sm">{message}</Text>
+      )}
+    </View>
+  );
+};