feat: shop detection from URL + vitest setup

tests/shops.test.ts

@@ -0,0 +1,22 @@
+import { describe, it, expect } from 'vitest'
+import { detectShop } from '@/lib/shops'
+
+describe('detectShop', () => {
+  it.each([
+    ['https://www.amazon.de/dp/B0C5BMMJTL', 'amazon'],
+    ['https://amazon.com/gp/product/B0C5BMMJTL', 'amazon'],
+    ['https://www.idealo.de/preisvergleich/OffersOfProduct/123456_-foo.html', 'idealo'],
+    ['https://geizhals.de/sony-playstation-5-a2362829.html', 'geizhals'],
+    ['https://www.geizhals.eu/foo', 'geizhals'],
+  ])('detects %s as %s', (url, expected) => {
+    expect(detectShop(url)).toBe(expected)
+  })
+
+  it('returns null for unknown shop', () => {
+    expect(detectShop('https://example.com/foo')).toBeNull()
+  })
+
+  it('returns null for invalid url', () => {
+    expect(detectShop('not a url')).toBeNull()
+  })
+})