Add workflow to check links with Lychee

.github/workflows/link-checker.yml

@@ -0,0 +1,29 @@
+name: Check Links
+
+on:
+  workflow_call:
+
+jobs:
+  linkChecker:
+    if: github.repository_owner == 'exercism'
+    runs-on: ubuntu-26.04
+    permissions:
+      issues: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1
+
+      - name: Link Checker
+        id: lychee
+        uses: lycheeverse/lychee-action@8646ba30535128ac92d33dfc9133794bfdd9b411
+        with:
+          args: --cache --accept ..=299,429 --suggest --verbose --require-https --user-agent "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.75 Safari/537.36" --no-progress **/*.md **/*.html **/*.toml **/*.json
+          fail: false
+
+      - name: Create Issue From File
+        if: steps.lychee.outputs.exit_code != 0
+        uses: peter-evans/create-issue-from-file@fca9117c27cdc29c6c4db3b86c48e4115a786710 # v6.0.0
+        with:
+          title: Link Checker Report
+          content-filepath: ./lychee/out.md
+          labels: report, automated issue

README.md

@@ -343,5 +343,31 @@ jobs:
       ordering: ".bucket, .slug"
 ```
 
+## Reusable workflow: link-checker
+
+The `link-checker` reusable workflow calls [Lychee][lychee] and creates an issue if any problematic links are reported.
+
+### Inputs
+
+None.
+
+### Example
+
+To run this on a monthly schedule, in your track repo add this workflow:
+
+```yaml
+name: Check Links
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: 0 0 15 * * # 15th day of each month
+
+jobs:
+  call-gha-workflow:
+    uses: exercism/github-actions/.github/workflow/link-checker.yml@main
+```
+
 [configlet]: https://exercism.org/docs/building/configlet
 [configlet-lint]: https://exercism.org/docs/building/configlet/lint
+[lychee]: https://github.com/lycheeverse/lychee#readme