check spelling in CI

.build.yml

@@ -1,6 +1,7 @@
 image: ubuntu/24.04
 packages:
   - imagemagick
+  - npm
   - rsync
   - ruby
 sources:
@@ -19,6 +20,8 @@ tasks:
       sudo apt install -y ./hugo_extended_0.122.0_linux-amd64.deb
       sudo gem install bundler
       echo 'cd davideisinger.com' >> ~/.buildenv
+  - spelling: |
+      npx cspell "content/**/*.md"
   - dither: |
       cd bin/dither
       sudo bundle install