fix: stop 'PlayCanvas Web Components' sidebar label wrapping

[willeastcott]

What changed

• Added className: 'sidebar-item-nowrap' to the PlayCanvas Web Components category in sidebars.js
• Added a matching CSS rule in src/css/custom.scss that applies white-space: nowrap to that item's sidebar link

Why

The 'PlayCanvas Web Components' sidebar label is borderline at the 310px sidebar width, so depending on OS/browser font metrics it sometimes rendered on one line and sometimes wrapped 'Components' onto a second line. This pins it to a single line everywhere.

Notes for reviewers

• The fix is scoped to this one item rather than all sidebar links, to avoid clipping risk on deeply nested labels. The class is reusable if other labels develop the same issue.
• There's comfortably enough horizontal room for the label on one line (~185px of text in ~240px of space), so nowrap won't overflow into the collapse caret.
• The CSS targets the rendered menu__link element, so the Japanese locale (shared sidebar structure) is covered too.

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