Add governance and onboarding docs

[dustenhubbard]

Problem

The repo lacks the standard governance and onboarding files a maintained, cited project is expected to have.

Proposed

Add SECURITY.md, .github/CODEOWNERS, .github/PULL_REQUEST_TEMPLATE.md, CONTRIBUTING.md, and CHANGELOG.md, adapted to the actual upstream setup (conda dev env, setup.py, Conventional Commits, squash-merge, PR + maintainer review).

Notes

Docs-only; no code changes. Security contact michael.chirillo@uri.edu; CODEOWNERS @quasiTriestino / @julian-falco.

Type:

Chore.