Add utilities and initial test coverage

src/platform/web.ts

@@ -0,0 +1,15 @@
+export const isOnline = () => {
+  if (typeof navigator !== 'undefined' && 'onLine' in navigator) {
+    return navigator.onLine;
+  }
+  return true;
+};
+
+export const triggerDownload = (blob: Blob, filename: string) => {
+  const url = URL.createObjectURL(blob);
+  const link = document.createElement('a');
+  link.href = url;
+  link.download = filename;
+  link.click();
+  URL.revokeObjectURL(url);
+};