Switch to checking for dead links in the docs/CI HTML via Lychee

.github/workflows/docs.yml

@@ -47,6 +47,12 @@ jobs:
         echo "url-count = ${{ steps.sitemap.outputs.url-count }}"
         echo "excluded-count = ${{ steps.sitemap.outputs.excluded-count }}"
 
+    - name: Linkcheck - Lychee
+      uses: lycheeverse/lychee-action@v2
+      with:
+        args: -c .lychee.toml build/install/docs/mfc/
+        fail: false
+
     - name: Publish Documentation
       if:   github.repository == 'MFlowCode/MFC' && github.ref == 'refs/heads/master' && ( github.event_name == 'cron' || github.event_name == 'workflow_dispatch' )
       run:  |

.lychee.toml

@@ -0,0 +1,17 @@
+# Maximum number of allowed retries before a link is declared dead.
+max_retries = 5
+
+# Don't show interactive progress bar while checking links.
+no_progress = true
+
+# Website timeout from connect to response finished.
+timeout = 20
+
+# Minimum wait time in seconds between retries of failed requests.
+retry_wait_time = 4
+
+# Comma-separated list of accepted status codes for valid links.
+# accept = ["200", "206", "403", "429"]
+accept = ["200", "429"]
+
+verbose = "error"