chore(deps): remove unmaintained broken-link-checker dev dependency (#255)

broken-link-checker@^0.7.8 is unmaintained (last released ~2017) and pulls in
a large legacy transitive tree (deprecated nopter, urlobj, urlcache, uuid@2
using Math.random, an old chalk/ansi stack), which is a needless security and
maintenance liability that drives Dependabot churn.

It was only exposed through the `npm run linkcheck` script and was never used
in CI. Local link checking is still possible via the better-maintained tools
documented in the docs repository (Antora xref-validator, htmltest,
filiph/linkcheck).

- drop the broken-link-checker devDependency
- drop the now-unused linkcheck npm script
- update agent/CLAUDE docs that referenced it to point at the documented tools
- regenerate package-lock.json (drops ~19 transitive packages)

Signed-off-by: Thomas Müller <1005065+DeepDiver1975@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: DeepDiver1975

agents.md

@@ -6,7 +6,7 @@ This file provides context for AI coding agents (Claude Code, GitHub Copilot, Cu
 - **Product family:** Documentation
 - **Primary language(s):** JavaScript
 - **Build system:** npm (Antora)
-- **Test framework:** broken-link-checker
+- **Test framework:** Antora build (`npm run antora`); link checking is documented in the `docs` repository
 - **CI system:** GitHub Actions
 
 ## Architecture & Key Paths
@@ -31,7 +31,8 @@ This file provides context for AI coding agents (Claude Code, GitHub Copilot, Cu
 npm run antora
 
 # Test
-npm run linkcheck
+# No automated test suite; verify by building (npm run antora).
+# Link checking is documented in the docs repository.
 
 # Lint
 Not detected (Prettier config present for formatting)