Studio: Ensure the add site screen can be dragged by the header

[katinthehatsite]

Related issues

Fixes STU-1076

Proposed Changes

This PR ensures that Studio app can be dragged by the top header when the user is on the Add site screen:

Testing Instructions

• Pull the changes from this branch
• Start the app with npm start
• Click on Add site
• Confirm that you can drag the app by the header

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[github-actions]

📊 Performance Test Results

Comparing 043bb7b vs trunk

site-editor

Metric	trunk	043bb7b	Diff	Change
load	9074.00 ms	10789.00 ms	+1715.00 ms	🔴 18.9%

site-startup

Metric	trunk	043bb7b	Diff	Change
siteCreation	23404.00 ms	22542.00 ms	-862.00 ms	🟢 -3.7%
siteStartup	10115.00 ms	9079.00 ms	-1036.00 ms	🟢 -10.2%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change

[katinthehatsite]

This will make the behaviour of the app consistent with other screens. One thing is that we don't have any visual indication where the header is on that screen but we would need reconsider design for that case.

[epeicher]

Thanks @katinthehatsite for fixing this! I have tested it, and it works as expected, I can move the Studio window when I'm adding a site. LGTM!

CleanShot.2025-12-11.at.10.22.38.mp4

[gavande1]

I tested it and it works as expected. LGTM 👍

CleanShot.2025-12-11.at.15.02.10.mp4