chore: Add link check action

[lbeckman314]

Overview ⚙️

Add automatic link checking action (and minor updates to header CSS + copyright footer)

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[Copilot]

Pull request overview

Adds automated link checking via a GitHub Action, along with small MkDocs presentation tweaks (header stacking and footer copyright display).

Changes:

• Add a new GitHub Actions workflow to run Lychee link checking on a schedule and on pushes.
• Update MkDocs footer copyright configuration.
• Adjust header z-index via custom CSS.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
mkdocs.yml	Adds a footer copyright string (currently using inline JS).
docs/stylesheets/extra.css	Raises .md-header stacking order via z-index.
.github/workflows/link-check.yml	Introduces a Lychee-based link check workflow + scheduled issue creation.

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[Copilot]

Inline <script> in the MkDocs config footer introduces executable JavaScript into every page. This can be blocked by CSP in some hosting setups and increases security risk compared to a build-time year. Prefer generating the year at build time via a theme template override (e.g., in an overrides/footer template using build_date_utc.year) or keep this as static text updated as needed.

Suggested change

	copyright: Copyright &copy; <script>document.write(new Date().getFullYear())</script> CALYPR
	copyright: "Copyright © 2026 CALYPR"

[Copilot]

The workflow header says it runs on pull requests, but the triggers only include push/workflow_dispatch/schedule. Add a pull_request trigger (optionally restricted to relevant paths) or update the comment to match the actual behavior.

[Copilot]

The schedule comment says “Sunday at 0 AM UTC”, but the cron expression (0 9 * * 0) runs at 09:00 UTC. Update either the comment or the cron value so they match.

Suggested change

	# Run weekly on Sunday at 0 AM UTC to catch external link changes
	# Run weekly on Sunday at 09:00 UTC to catch external link changes

[Copilot]

Workflow permissions are broader than necessary: nothing in this workflow currently uses pull-requests: write, and issues: write is only needed for the scheduled run that creates an issue. Consider removing pull-requests: write and scoping issues: write to only the job/step that needs it (or guarding via a separate job) to follow least-privilege.

Suggested change

	pull-requests: write
	issues: write
	jobs:
	lychee:
	runs-on: ubuntu-latest
	jobs:
	lychee:
	runs-on: ubuntu-latest
	permissions:
	contents: read
	issues: write

[Copilot]

The args/comment don’t match: the comment says only docs/ and README.md, but the args include '**/*.md' which already covers those and will also scan every Markdown file in the repo. Either drop the redundant globs or update the comment (and consider restricting to the intended paths to reduce runtime/noise).

Suggested change

	# Check all markdown files in docs/ and README.md
	args: --verbose --no-progress --exclude-private 'docs/**/*.md' 'README.md' '**/*.md'
	# Check all Markdown files in the repository
	args: --verbose --no-progress --exclude-private '**/*.md'