Fix e2e test: Update date button selector to use data-testid

- Replace text-based selector that expected English weekdays with data-testid selector
- Dates now use Spanish locale (es-ES) formatting, so weekday text changed
- Using data-testid is more reliable and language-agnostic
- Fixes failing test: 'regular user can access exchange page, all UI elements work, and buy/sell toggle functions'

frontend/e2e/exchange.spec.ts

@@ -97,10 +97,12 @@ test.describe("Exchange Page - Regular User Access", () => {
     // Test date selection appears after continue
     await page.getByRole("button", { name: "Continue to Booking" }).click();
     await expect(page.getByRole("heading", { name: "Select a Date" })).toBeVisible();
-    const dateButtons = page
-      .locator("button")
-      .filter({ hasText: /^(Mon|Tue|Wed|Thu|Fri|Sat|Sun)/ });
-    await expect(dateButtons.first()).toBeVisible();
+    // Date formatting uses Spanish locale (es-ES), so weekdays are in Spanish: Lun, Mar, Mié, Jue, Vie, Sáb, Dom
+    // Use data-testid selector which is more reliable than text matching
+    // Wait for at least one date button to appear (they have data-testid="date-YYYY-MM-DD")
+    await expect(page.locator('button[data-testid^="date-"]').first()).toBeVisible({
+      timeout: 10000,
+    });
   });
 });