fix: resolve react-hooks/purity ESLint error in sidebarmenuskeleton

[naaa760]

PR Description for #8540

Fix react-hooks/purity ESLint error in SidebarMenuSkeleton component

• Problem: The react-hooks/purity ESLint rule was flagging an error because Math.random() was being called inside a useMemo hook during render, which violates React's purity requirements.

• Solution: Converted useMemo to useState with lazy initialization to ensure the random width calculation only happens once during component initialization, not on every render.

Changes made:

• Updated SidebarMenuSkeleton component in all three variants (v4, www/default, www/new-york)
• Replaced useMemo(() => Math.random()...) with useState(() => Math.random()...)
• Added appropriate ESLint disable comment as per the suggested fix

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[github-actions]

Looks like this PR modifies files in apps/www, which is deprecated.

Consider applying the change to apps/v4 if relevant.