Display Pages Sidebar template content at default width in editor

[moonjellydigital]

Description

Fixes issue #136, content in the editor displayed at excessive width when the Pages Sidebar template is applied.

Screenshots

	Before	After
Editor view

Testing Instructions

1. Open a page in the post editor or the Site Editor, through Site Editor > Pages > Edit.
2. Change the template to Pages Sidebar.
3. Check that content is the default content width, not expanded to full width.

Use of AI Tools

AI assistance: No

[github-actions]

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[github-actions]

👋 Thanks for your first pull request, @moonjellydigital! We'll take a look soon.