Refactor Playwright tests in dag-calendar-tab (#63409)

[snesan821]

Description

This PR addresses Playwright testing anti-patterns outlined in Issue #63409, specifically focusing on the DagCalendarTab page object.

Changes:

• Removed deprecated page.waitForFunction() DOM query used to count calendar cells.
• Implemented web-first assertion (expect(locator).toBeVisible()) utilizing existing calendarCells locator to ensure the calendar grid is fully loaded and stable.

closes: #63409

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Was generative AI tooling used to co-author this PR?

• Yes (Kiro Agentic IDE)

Generated-by: Kiro following the guidelines

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[boring-cyborg]

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[choo121600]

Would it make sense to switch these to expect().toBeVisible() instead of waitFor()?
This could make the test more explicit and rely on Playwright’s built-in retry + assertion behavior.

[snesan821]

Hey @choo121600, thanks for the review! That completely makes sense. I've updated the DagCalendarTab tests to use expect().toBeVisible() (and toBeHidden()) to leverage Playwright's built-in web-first assertions and retry behavior.

Just a heads-up: while making this update, I also included a few targeted stability patches in this push to help resolve the Playwright WebKit E2E test flakes we were seeing fail the CI. These changes mostly involve adding explicit DOM readiness waits and relaxing some brittle timeouts across DagsPage, RequiredActionsPage, ConnectionsPage, and XComsPage.

Let me know if everything looks good to go now!