add centralized error handling and improve Google Auth error logging

src/services/ErrorHandler.js

@@ -0,0 +1,36 @@
+import { Alert } from 'react-native';
+
+/**
+ * Centralised error handler for the app.
+ *
+ * Usage:
+ *   import { logError, alertError } from '../services/ErrorHandler';
+ *
+ *   logError('Google Auth', error);          // console.error only
+ *   alertError('Upload Failed', error);      // Alert + console.error
+ */
+
+/**
+ * Log an error to the console with a contextual tag.
+ * @param {string} tag   – short label, e.g. 'Google Auth', 'NAS'
+ * @param {Error|string} error
+ */
+export const logError = (tag, error) => {
+  const message = error instanceof Error ? error.message : String(error);
+  console.error(`[${tag}] ${message}`);
+};
+
+/**
+ * Show a user-facing Alert AND log to the console.
+ * @param {string} title – Alert title
+ * @param {Error|string} error
+ * @param {Array}  [buttons] – optional Alert button array
+ */
+export const alertError = (title, error, buttons) => {
+  const message = error instanceof Error ? error.message : String(error);
+  console.error(`[${title}] ${message}`);
+  Alert.alert(title, message, buttons || [{ text: 'OK' }]);
+};
+
+export default { logError, alertError };
+