e2e test - "Clear the current URL" button clears the Viewer pane

[rodrigosf672]

Adds a test step to confirm that Clear Current URL removes the active iframe and resets the Viewer.

Why test.step()

• Keeping it inside the existing Dash test avoids extra setup and follows the same pattern as other Viewer checks (e.g., open-in-editor).
• It fits cleanly into the app’s lifecycle without creating new tests (less time spent running tests).
• Note that the step is placed in the end of the test. Changing the order of steps in the future could lead to failure of other steps.

Why only in the Dash app

• The feature is Viewer-specific, not app-specific, so duplicating it across other Python apps offers no extra coverage.
• Dash is the simplest, most stable example, and its clear “Hello World” render allows the test to reliably assert the iframe to no-iframe state transition (from occupied iframe to div-content emptiness).
• If test.step() fails in the future, the presence of "Hello World" would be a clear indicator to look at the screenshots.

QA Notes

@:apps @:viewer @:editor @:web

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical @:apps @:viewer @:editor @:web

^{readme  valid tags}

[testlabauto]

LGTM!

[testlabauto]

Any idea why its not passing?