fix: add SECRET_KEY env to deploy job for compose expansion

Container runtime needs SECRET_KEY in the shell environment so docker
compose can expand ${SECRET_KEY} from the compose file.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/deploy-dev.yml

@@ -161,6 +161,8 @@ jobs:
     name: Deploy to Dev
     runs-on: ubuntu-latest
     needs: [backend-tests, frontend-tests]
+    env:
+      SECRET_KEY: test-secret-key-for-ci-environment-32chars-minimum
     container:
       volumes:
         - /var/packages/ContainerManager/target/usr/bin/docker:/usr/bin/docker