Gitignore local build and publish artifacts

Ignore VERSION, cover image, vendor bundle, and Gemfile.lock
used by the local publish pipeline on the build server.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: happi

.gitignore

@@ -29,3 +29,6 @@ site
 .DS_Store
 /VERSION
 /images/cover.jpg
+/vendor/
+/.bundle/
+/Gemfile.lock