fix(e2e): use unique plate in QR code test to avoid admin row collision

The new 'shows QR code for desktop scanning' E2E test used plate JKL012,
which is the same plate seeded as a processing order in the dev migrations
(V7__seed_processing_order.sql) and used by the admin dashboard/fulfillment
tests as PROCESSING_PLATE.

Because the E2E chromium (parallel) tests run before the chromium-serial
tests, the QR test created a second order with plate JKL012. When the serial
admin tests then searched for rows matching JKL012, Playwright's strict
mode found 2 matching rows and threw a strict mode violation.

This caused 4 test failures + 2 skipped tests:
- admin-dashboard: click row shows tracking section
- admin-dashboard: click row again collapses it
- admin-dashboard: expanded row shows tracking input and save button
- admin-fulfillment: can register shipment for processing order
- admin-fulfillment: can mark sent order as delivered (skipped)
- admin-fulfillment: can mark delivered order as failed then back to sent (skipped)

Changed the plate to QRA222 — not used in any seed data or other E2E test.

frontend/e2e/payment-redirect.spec.ts

@@ -55,7 +55,7 @@ test.describe('Payment redirect', () => {
   })
 
   test('shows QR code for desktop scanning', async ({ page }) => {
-    await page.goto('/compose?plate=JKL012')
+    await page.goto('/compose?plate=QRA222')
     await page.getByLabel('Ditt meddelande').fill('Fin bil!')
     await page.getByRole('button', { name: 'Fortsätt till betalning' }).click()