Add utility functions and unit tests

src/utils/format.ts

@@ -0,0 +1,17 @@
+export function formatDate(iso: string): string {
+  return new Intl.DateTimeFormat('de-DE', {
+    day: '2-digit', month: '2-digit', year: 'numeric',
+  }).format(new Date(iso));
+}
+
+export function truncate(str: string, maxLen: number): string {
+  return str.length <= maxLen ? str : str.slice(0, maxLen - 1) + '…';
+}
+
+export function bytesToHuman(bytes: number): string {
+  const units = ['B', 'KB', 'MB', 'GB'];
+  let n = bytes;
+  let i = 0;
+  while (n >= 1024 && i < units.length - 1) { n /= 1024; i++; }
+  return `${n.toFixed(1)} ${units[i]}`;
+}

tests/format.test.ts

@@ -0,0 +1,12 @@
+import { describe, it, expect } from 'vitest';
+import { truncate, bytesToHuman } from '../src/utils/format';
+
+describe('truncate', () => {
+  it('leaves short strings alone', () => expect(truncate('hi', 10)).toBe('hi'));
+  it('truncates long strings', () => expect(truncate('hello world', 7)).toBe('hello w…'));
+});
+
+describe('bytesToHuman', () => {
+  it('formats bytes', () => expect(bytesToHuman(1024)).toBe('1.0 KB'));
+  it('formats megabytes', () => expect(bytesToHuman(1536 * 1024)).toBe('1.5 GB'));
+});