fix(test): remove unused variable in e2e test

tests/test_e2e_playwright.py

@@ -348,13 +348,6 @@ def test_backtest_page_handles_invalid_dates_gracefully() -> None:
         page.wait_for_timeout(2000)
         
         # Should show validation error or prevent running, not crash
-        # Check for validation message
-        has_validation = (
-            page.locator("text=Invalid start date").is_visible() or
-            page.locator("text=data available from").is_visible() or
-            page.locator("text=warning").is_visible()
-        )
-        
         # Verify no 500 error
         error_500 = page.locator("text=500").count()
         assert error_500 == 0, "Page should not show 500 error for invalid dates"