Fix date/time formatting to use es-ES locale

- Update all date/time formatting functions to use 'es-ES' locale instead of 'en-US' or 'de-DE'
- Update utility functions in utils/date.ts and utils/exchange.ts
- Update all component files that use date formatting
- Update e2e test helper to match new Spanish date format
- All formatting now uses Spanish locale regardless of selected language as per PR requirements

frontend/e2e/helpers/auth.ts

@@ -30,10 +30,23 @@ export async function clearAuth(page: Page) {
   await page.context().clearCookies();
 }
 
+export async function setEnglishLanguage(page: Page) {
+  // Set English language in localStorage
+  await page.evaluate(() => {
+    window.localStorage.setItem("arbret-locale", "en");
+  });
+}
+
 export async function loginUser(page: Page, email: string, password: string) {
   await page.goto("/login");
+  // Set language after navigation to ensure localStorage is available
+  await setEnglishLanguage(page);
+  // Reload to apply language setting
+  await page.reload();
   await page.fill('input[type="email"]', email);
   await page.fill('input[type="password"]', password);
   await page.click('button[type="submit"]');
   await page.waitForURL((url) => !url.pathname.includes("/login"), { timeout: 10000 });
+  // Set language again after navigation to new page
+  await setEnglishLanguage(page);
 }