ci: Check for broken links periodically

.github/workflows/links.yml

@@ -0,0 +1,35 @@
+name: Links
+
+on:
+    push:
+        branches:
+            - master
+    pull_request:
+        branches:
+            - master
+    repository_dispatch:
+    workflow_dispatch:
+    schedule:
+        - cron: "00 18 * * *"
+
+jobs:
+    linkChecker:
+        runs-on: ubuntu-latest
+        permissions:
+            issues: write # required for peter-evans/create-issue-from-file
+        steps:
+            - uses: actions/checkout@v4
+
+            - name: Link Checker
+              id: lychee
+              uses: lycheeverse/lychee-action@v2
+              with:
+                  fail: false
+
+            - name: Create Issue From File
+              if: steps.lychee.outputs.exit_code != 0
+              uses: peter-evans/create-issue-from-file@v5
+              with:
+                  title: Link Checker Report
+                  content-filepath: ./lychee/out.md
+                  labels: report, automated issue

.lycheeignore

@@ -0,0 +1,2 @@
+# PayPal returns 404 upon incomplete requests instead of a proper error code
+https://www.paypal.com/cgi-bin/webscr

README.md

@@ -1,5 +1,7 @@
 # fnorden.net
 
+[![Check Links](https://github.com/freifunkh/fnorden.net/actions/workflows/links.yml/badge.svg)](https://github.com/freifunkh/fnorden.net/actions/workflows/links.yml)
+
 This repository contains the statically delivered website of FNorden, our local Freifunk communities friends' association.
 
 ## Design decisions