[CI] Integrate lychee action for links availability checks (#742)

Author: aobolensk

.github/workflows/pre-commit.yml

@@ -19,6 +19,17 @@ jobs:
           post_comment: false
           fail_on_find: true
 
+  link-check:
+    if: github.repository == 'learning-process/parallel_programming_course'
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v6
+      - name: Check links
+        uses: lycheeverse/lychee-action@v2
+        with:
+          fail: true
+          failIfEmpty: false
+
   pre-commit:
     needs: check-file-sizes
     runs-on: ubuntu-24.04

.lycheeignore

@@ -0,0 +1,3 @@
+# Ignore URL-encoded Jinja template placeholders from Sphinx HTML templates.
+# These are not real links and are resolved only during docs build.
+file://.*/%7B%7B.*%7D%7D.*