add profile screens to Library navigation

[panaC]

Fixes #3902
Fixes #3904

• Add customization profile rel="screen" links to the Library navigation.
• Introduce /profile/:screenId routes with browser history support.
• Select screens using the current locale, with English and language-neutral fallback.
• Restrict screen loading to resources declared by the active profile manifest.
• Sanitize profile HTML and enforce scoped CSS and Thorium typography.
• Add loading, error, redirect, request cancellation, and heading-focus handling.
• Track generic Profile Page and Profile Catalog page_view events without exposing profile identifiers.
• Track successful profile activation with profile_activate.
• Document the profile-screen authoring contract.

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	css-selector-parser@​3.3.0

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