ci: fix broken vnu download and linkedin link-check 404

Both CI jobs (Validate HTML and Check Links) had been red on main since
the v2.1.0 docs sync. Two unrelated infra issues, both fixed.

Validate HTML: the validator/validator GitHub project does not publish
Releases (only tags), so the install URL
github.com/validator/validator/releases/latest/download/vnu.jar_dist.zip
404s and unzip exits 9 before vnu ever runs. Switch to the official
vnu-jar npm package (currently v26.4.16). It bundles vnu.jar at a stable
known path under node_modules. Drop the apt install of default-jre too;
ubuntu-latest runners ship with Java preinstalled.

Check Links: linkedin.com/in/savvides/ 404s for unauthenticated bot
requests. The link itself is correct and works in browsers. Add
--exclude linkedin.com to the lychee args.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: savvides

.github/workflows/ci.yml

@@ -14,15 +14,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Install vnu
-        run: |
-          sudo apt-get update -qq
-          sudo apt-get install -y -qq default-jre
-          curl -sL https://github.com/validator/validator/releases/latest/download/vnu.jar_dist.zip -o vnu.zip
-          unzip -q vnu.zip
+      - name: Install vnu-jar
+        run: npm install --no-save vnu-jar
 
       - name: Validate HTML
-        run: java -jar dist/vnu.jar --errors-only index.html
+        run: java -jar node_modules/vnu-jar/build/dist/vnu.jar --errors-only index.html
 
   check-links:
     name: Check Links
@@ -34,5 +30,5 @@ jobs:
       - name: Check links
         uses: lycheeverse/lychee-action@v2
         with:
-          args: --exclude fonts.googleapis.com --exclude fonts.gstatic.com --exclude d3js.org --exclude localhost --no-progress index.html README.md
+          args: --exclude fonts.googleapis.com --exclude fonts.gstatic.com --exclude d3js.org --exclude linkedin.com --exclude localhost --no-progress index.html README.md
           fail: true