Delete site confirmation layout is broken in agentic UI

[katinthehatsite]

Related issues

Fixes STU-1921

How AI was used in this PR

Not needed

Proposed Changes

This PR ensures that the layout of the delete confirmation dialog for a site has appropriate paddings and margins.

Before

After

Testing Instructions

• Pull the changes from this branch
• Start Studio with npm start
• Enable the Agentic UI feature flag from Studio -> Feature flags from the topbar
• Click on the ellipsis menu by a site
• Select an option to delete a site
• Confirm that the dialog to delete a site has correct margins and paddings

Pre-merge Checklist

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

[gavande1]

LGTM 👍

[wpmobilebot]

📊 Performance Test Results

Comparing 6278095 vs trunk

app-size

Metric	trunk	6278095	Diff	Change
App Size (Mac)	1419.29 MB	1419.29 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	6278095	Diff	Change
load	1090 ms	742 ms	348 ms	🟢 -31.9%

site-startup

Metric	trunk	6278095	Diff	Change
siteCreation	6528 ms	6986 ms	+458 ms	🔴 7.0%
siteStartup	2393 ms	2403 ms	+10 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)