1.3 Create CI Pipeline Test Stage

Summary

• Add .test_node hidden template with NODE_ENV: test and shared artifact defaults
• Create 4 new test jobs: test:backend, test:frontend, test:doc-repo, test:python
• Update flutter:test (remove duplicate flutter analyze, add main branch rule)
• All 5 test jobs run in parallel in the test stage with path-based rules:changes + main branch rule
• JUnit XML reports collected as artifacts:reports:junit (4/5 — Flutter pending junitreport from story 1-1)

Test plan

• Verify YAML syntax: python3 -c "import yaml; yaml.safe_load(open('.gitlab-ci.yml'))"
• Verify lint jobs and patrol:e2e are unchanged
• Verify all 5 test jobs are in test stage and run in parallel
• Verify all Node.js jobs have NODE_ENV: test
• Verify all jobs have cache with test-* prefixes
• Verify all jobs have path-based rules:changes for MRs + main branch rule