fix: Add Composer auth for private repository in CI

Use COMPOSER_AUTH with HTTP basic auth to access private
wc-licensed-product-client repository during builds.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -30,6 +30,8 @@ jobs:
         run: composer validate --strict
 
       - name: Install Composer dependencies (production)
+        env:
+          COMPOSER_AUTH: '{"http-basic": {"src.bundespruefstelle.ch": {"username": "git", "password": "${{ secrets.SRC_GITEA_TOKEN }}"}}}'
         run: |
           composer config platform.php 8.3.0
           composer install --no-dev --optimize-autoloader --no-interaction