feat(mdx/image): Add dead image detection

[elliotcourant]

Summary

I noticed during builds that if dead image links were used that they did not necessarily produce a warning. But dead links would. This copies the pattern used for dead link detection and basically applies it to images as well. But does not do anything for external images, only local ones.

Related Issue

N/A

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[elliotcourant]

Still need to update documentation, working on that now

[Copilot]

Pull request overview

Adds dead local image detection to the MDX pipeline, mirroring the existing dead link detection behavior, with configurable options exposed via markdown.image.

Changes:

• Introduces RemarkImageOptions (checkDeadImages with optional excludes) and wires it into MarkdownOptions.
• Extends the remarkImage plugin to detect missing local images (absolute-from-public and relative-to-doc) and fail builds in production (or report via lint).
• Adds unit tests covering existing/missing absolute & relative images and external image behavior; plumbs the new options through MDX options creation (disabled for isSsgMd).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/shared/src/types/index.ts	Adds RemarkImageOptions and exposes markdown.image config.
packages/core/src/node/mdx/remarkPlugins/image.ts	Implements dead local image detection and reporting/throwing logic.
packages/core/src/node/mdx/remarkPlugins/image.test.ts	Adds tests for dead-image detection behavior.
packages/core/src/node/mdx/options.ts	Passes docDirectory + markdown.image options into remarkImage (disabled for SSG-md).

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[elliotcourant]

I've updated part of the docs, but only the english version

[SoonIter]

LGTM, thanks ❤️️