Validate and update links (STF-557)

[oschwald]

Adds a lychee link checker configuration and a CI
workflow (.github/workflows/links.yml), and fixes stale/redirecting links
surfaced by the check.

Setup

• lychee.toml with max_redirects = 0 (canonical-URL enforcement) and the
  shared MaxMind accept/exclude lists.
• Minimal mise.toml pinning lychee = "0.23.0" plus a check-links task
  (globs: './**/*.md' './src/**/*.php' './composer.json').
• .github/workflows/links.yml runs lychee via mise (install: false +
  MISE_AUTO_INSTALL: false, so only lychee is installed, not the full
  toolchain). Scheduled weekly to catch external link rot.
• .lycheecache added to .gitignore.

Link fixes

• composer.json author homepage: https://www.maxmind.com/ -> https://www.maxmind.com/en/home
• README.md Fedora package page: https://apps.fedoraproject.org/packages/php-maxminddb -> https://packages.fedoraproject.org/pkgs/php-maxminddb/php-maxminddb/
• README.md EPEL repository: https://fedoraproject.org/wiki/EPEL -> https://docs.fedoraproject.org/en-US/epel/
• README.md libmaxminddb tarball anchor: .../README.md#installing-from-a-tarball -> .../README.md#from-a-named-release-tarball
• README.md support page: https://www.maxmind.com/en/support -> https://support.maxmind.com/knowledge-base

Final lychee run: 13 OK, 0 errors, 1 excluded.

Part of STF-557.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request configures the Lychee link checker by adding .lycheecache to .gitignore, creating lychee.toml and mise.toml configurations, and updating several outdated URLs in README.md and composer.json. The review feedback suggests removing 5xx status codes from the accepted list in lychee.toml to prevent permanently broken links from being silently ignored.

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[gemini-code-assist]

Accepting all 5xx server errors (500..=599) defeats the purpose of link checking, as permanently broken links returning internal server errors or bad gateways will be silently ignored. It is better to remove 500..=599 from the accept list. If temporary network issues or rate limits are a concern, consider using lychee's retry mechanism or excluding specific flaky domains instead.

Suggested change

	# 500-599: Server errors (temporary issues shouldn't fail CI)
	# 999: LinkedIn's custom status code
	accept = ["100..=103", "200..=299", "403", "429", "500..=599", "999"]
	# 999: LinkedIn's custom status code
	accept = ["100..=103", "200..=299", "403", "429", "999"]

[oschwald]

Keeping 500..=599 in accept, matching the dev-site and blog-site configs — transient upstream 5xx shouldn't fail link-checking CI.

— Claude (posted on Greg's behalf)