Fix: Update iframe selector to use 'preview-iframe' class

[leandrowilliam]

The 'Open in New Tab' button was not working because it was looking for an iframe with class 'preview', but the UI revamp changed it to 'preview-iframe'. This updates the JavaScript selector to match.

• Update to in open-preview click handler
• Update to in refreshPreview function

Fixes the bug where clicking 'Open in New Tab' opened a blank page.

Closing issues: #1452

Before	After

[leandrowilliam]

@ricardo-devis-agullo I was tempted to write a unit test like this in registry-ui.js:

    it('should have matching iframe element and JavaScript selector for preview functionality', () => {
      const hasIframeElement = result.includes('class="preview-iframe"');
      const hasMatchingJavaScript = result.includes("$('.preview-iframe')");
      
      expect(hasIframeElement).to.be.true;
      expect(hasMatchingJavaScript).to.be.true;
    });

However, I feel this test would be quite specific and fragile, testing implementation details (JS/HTML/CSS class matching) rather than the actual functionality. I'm not sure if it's worthwhile.
To properly test the "Open in New Tab" functionality, we'd need browser automation (like Playwright or Puppeteer) to verify that clicking the button actually opens a new tab with the correct URL. I looked through the codebase but couldn't find any existing browser testing setup, and I'm not sure if adding such infrastructure would be appropriate for this simple bug fix.
What do you think? Should I add the test above, look into setting up browser testing, or keep this PR focused just on the bug fix?

[ricardo-devis-agullo]

thanks for the fix! I'd say we can merge this. Doing e2e tests to test the whole UI is nice but is a bigger story than this fix. There is technically a new file in preview/uiPreview.ts that you can run with Bun that starts a mocked local registry that you could attach playwright too, but its something that I might take on myself so no worries!

[leandrowilliam]

Cool, sounds good!