ci: decode SSH key from base64 in deploy stage

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

.gitlab-ci.yml

@@ -41,7 +41,7 @@ deploy_production:
     - build
   before_script:
     - eval $(ssh-agent -s)
-    - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add -
+    - echo "$SSH_PRIVATE_KEY" | base64 -d | ssh-add -
     - mkdir -p ~/.ssh
     - echo "$SSH_KNOWN_HOSTS" >> ~/.ssh/known_hosts
     - chmod 644 ~/.ssh/known_hosts