docs: add contributor self-review template

[vickman787]

Issue Reference

Closes #513

Summary

Adds a copy-paste Contributor Self-Review Template (docs/self-review-template.md) covering behaviour, tests, CI, security, edge cases, and docs impact, for contributors to run through before opening a PR. Links it from the PR template, README, and CONTRIBUTING.md, and cross-references it from the existing Contribution Quality Gate.

Contract Functions Changed

none (documentation-only change)

Tests Added or Updated

none — documentation-only change, no contract logic touched.

Security Considerations

No security impact — documentation-only change, no contract code touched.

Commands Run

N/A — documentation-only change; no build/test/lint surface touched.

Traceability Table

Criterion ID	Criterion Text	Changed Function(s)	Test(s)	Edge Cases Covered	Status
AC-1	Self-review template is added	—	—	—	Met — docs/self-review-template.md
AC-2	Behaviour requirements are covered	—	—	—	Met — "Behaviour" section of the template
AC-3	Security and edge cases are covered	—	—	—	Met — "Security" and "Edge cases" sections of the template
AC-4	Tests and CI are covered	—	—	—	Met — "Tests" and "CI" sections of the template
AC-5	Docs impact is included	—	—	—	Met — "Docs" section of the template
AC-6	README links to the template	—	—	—	Met — added under README Documentation list and Contributing section