Add lychee link checker

[cnaples79]

Summary

• add a GitHub Actions workflow to run lychee for broken-link checks on docs/content changes
• schedule a weekly run and allow manual dispatch

Rationale

Automated link checking helps catch broken links early without relying on manual checks.

Changes

• new GH action using lycheeverse/lychee-action with PR/scheduled/manual triggers

Test Plan

• not run (workflow addition only)

Fixes #134

[dlebauer]

@cnaples79 thanks for this contribution! I added a few components from the version in the SIPNET repository. Need to confirm that this works before merging; feel free to remove problematic args that I suggested.

[dlebauer]

These settings were helpful in the SIPNET link checker - mostly in making the workflow more robust to common non-errors. Please consider whether they will be helpful here.

Suggested change

	args: "--verbose --no-progress --exclude-mail"
	args: >-
	--verbose --no-progress --exclude-mail
	--include-fragments
	--no-progress
	--verbose
	--timeout 20
	--max-redirects 10
	--max-retries 3
	--retry-wait-time 2
	--format markdown
	--exclude '^https://doi\.org/'
	.
	fail: true

[dlebauer]

remove --include-fragments initially (or add exclusions). if problematic.

[dlebauer]

Suggested change

	GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
	GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
	- name: Upload lychee report
	if: ${{ always() }}
	uses: actions/upload-artifact@v4
	with:
	name: lychee-report
	path: lychee

[dlebauer]

@cnaples79 I ran the workflow (without my suggestions) and it passed. But we have three current issues open that reported broken links: #60, #136, and #137.

Do you know why this would be or what the fix would be?

This PR should fix those broken link issues and close #135

Thanks again for your help with this!

[dlebauer]

Note - once this is merged we should consider whether we should re-enable the rule that requires the link checker to pass before merging PRs, or how we should be notified.