Import template community files and add dsagt-adapted CI workflow

[Copilot]

Summary

This PR brings in the requested repository boilerplate from the template effort and adds missing community/process files to dsagt. It also introduces a GitHub Actions CI workflow adapted to this repo’s standards (ruff + Python 3.12/3.13 non-integration test matrix).

• Repository governance/docs

  • Added CHANGELOG.md, CONTRIBUTING.md, SECURITY.md, CODE_OF_CONDUCT.md
  • CONTRIBUTING.md includes external contributor workflow plus AI/LLM-assisted contribution guidance

• GitHub templates

  • Added .github/ISSUE_TEMPLATE/bug_report.md
  • Added .github/ISSUE_TEMPLATE/feature_request.md
  • Added .github/pull_request_template.md

• CI workflow alignment

  • Added .github/workflows/ci.yml
  • Lint job uses ruff
  • Test job runs on Python 3.12 and 3.13 with non-integration tests

strategy:
  matrix:
    python-version: ["3.12", "3.13"]
...
run: python -m pytest -m "not integration" -q

Related Issue

Issue linking is handled automatically.

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / maintenance

Validation

• Local linting completed
• Relevant tests added/updated
• Relevant tests passed

Checklist

• I followed repository contribution guidance
• I updated docs where needed
• I confirmed no secrets or credentials were added