merge template repo updates

[shreddd]

Bring in various boilerplate files from https://github.com/AI-ModCon/BaseTemplate

[shreddd]

Bring in the following based on initial assessment from Claude:

1. .github/ directory

• workflows/ci.yml — GitHub Actions CI with lint + multi-Python-version test matrix. Needs adaptation (use dsagt's ruff, instead and target dsagt's Python 3.12–3.13 range).
• ISSUE_TEMPLATE/bug_report.md — structured bug report template
• ISSUE_TEMPLATE/feature_request.md — feature request template
• pull_request_template.md — PR checklist template

2. CHANGELOG.md — dsagt has none; standard community file
3. CONTRIBUTING.md — dsagt only has developer.md (internals-focused). CONTRIBUTING covers external contributor workflow, PR/commit style, and notably has a good AI/LLM-assisted contributions section. Worth adding separately from developer.md.
4. SECURITY.md — dsagt has none
5. CODE_OF_CONDUCT.md — generic Contributor Covenant boilerplate