Fix close modal when adding a blank site

[sejas]

Related issues

• Fixes STU-1072
• Related Replace empty screen with add site flow and rename it to NoStudioSites #2149

Proposed Changes

• Make sure the add site modal closes after creating the site

Testing Instructions

• Click on "Add Site" in the left sidebar.
• Click on "Create a blank site"
• Continue the process
• Observe that the modal closes the moment that you click the last "Add site" button

Pre-merge Checklist

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

[github-actions]

📊 Performance Test Results

Comparing 2cc30b2 vs trunk

site-editor

Metric	trunk	2cc30b2	Diff	Change
load	13075.00 ms	16841.00 ms	+3766.00 ms	🔴 28.8%

site-startup

Metric	trunk	2cc30b2	Diff	Change
siteCreation	23591.00 ms	22911.00 ms	-680.00 ms	🟢 -2.9%
siteStartup	10052.00 ms	9028.00 ms	-1024.00 ms	🟢 -10.2%

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Results are median values from multiple test runs.

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

[sejas]

E2E had a timeout on Windows: 1) e2e\site-navigation.test.ts:100:6 › Site Navigation › creates a post