Slaif fixes

[janezd]

• Limit the width of the content index to prevent it to be mostly to the left of the window in case of long titles.
• Fix copy to clipboard in Expressive Code elements.
• Remove Expressive Code terminal frames.
• Fix sizing of Expressive Code elements (in particular, excluding horizontal scrollbars from calculation)

[Copilot]

Pull request overview

This PR addresses several UX and rendering issues related to the Content Index positioning and rehype-expressive-code output in rendered MDX, including copy-to-clipboard behavior and terminal styling.

Changes:

• Adds a client-side copy-to-clipboard initializer for Expressive Code copy buttons and wires it into the Book page.
• Removes Expressive Code “terminal frame” styling by stripping the is-terminal class during ingestion.
• Constrains the header content-index width to prevent it from shifting off-screen with long titles.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
utils/copyToClipboard.ts	Adds DOM-based copy button wiring with Clipboard API + fallback.
components/Book/Book.tsx	Runs Expressive Code “init” logic on mount and on DOM mutations to support MDX-rendered content.
ingest/plugins.ts	Introduces a rehype plugin that removes the is-terminal class from output.
ingest/md-helpers.ts	Registers the new rehype plugin in the MDX compilation pipeline.
styles/content-index/content-index.scss	Adds a max-width to keep the header content index from becoming too wide.

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