Grant contents: write to deploy workflow so site-deploy can push gh-pages

The permissions block added in 5a8f948 only granted packages: write,
which drops the GITHUB_TOKEN's contents scope. maven-scm-publish-plugin
then fails to push the site to gh-pages with a 403.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: udaw

.github/workflows/deploy.yml

@@ -8,6 +8,7 @@ on:
     branches: [ master ]
 
 permissions:
+  contents: write
   packages: write
 
 jobs: