feat: update gh-pages workflows

[jaeheonji]

This PR aims to address several issues currently present in our repository:

• Our website relies on two components: Hugo and mdBook.
• Currently, only the Hugo build is included in our workflows. Therefore, when there are changes to the documentation, we must build it locally and include the generated files in the MR.
• After the gh-pages branch is created, the CNAME file must be manually committed.
• The workflow runs every time there’s a push to the main branch, which can lead to unexpected deployments.

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cc: @imsnif
related: #274

[Copilot]

Pull Request Overview

This PR enhances the GitHub Pages deployment workflow by adding mdBook documentation build support and optimizing CI triggers. The workflow now builds mdBook documentation before Hugo, and only runs when relevant content files change.

• Added mdBook build step to generate documentation into the static directory
• Configured path-based workflow triggers to run only when documentation, content, SVG, or layout files change
• Added CNAME configuration for custom domain deployment

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