Add lightweight contributor workflow for “good first issue” / “help w…

[Machumerre]

Adds a concise Contributor Workflow section to CONTRIBUTING.md that guides new contributors through picking a small issue, commenting before work, keeping the PR focused, running repository-specific validation, and reporting skipped slow checks. No code or CI changes are made.

Fixes #27

Validation

• git diff --check passes.
• Reviewed the updated Markdown text in CONTRIBUTING.md for repository-specific npm validation guidance.
• Broader build/test checks were not run because this is a documentation-only contributor workflow update.

[aoto-tech]

Thanks for the contribution. The scope looks good, but the validation guidance needs to match this repository before merging.

Please address the following:

1. Replace make test / pytest -q with the npm-based validation commands already documented above in CONTRIBUTING.md.

2. Clarify that contributors should run targeted checks first, without implying that required checks can simply be skipped. For documentation-only changes, smaller validation is acceptable when explained in the PR.

3. Add Fixes #27 and a short validation section to the PR description. Report the checks you actually performed and explicitly state any checks you did not run. Please also confirm that the updated Markdown renders correctly.

Please keep the changes limited to this contributor guide.

[aoto-tech]

@Machumerre Thanks for the contribution. I cannot merge this as-is because it does not clearly reference the target issue and the suggested validation commands do not match this repository (make test / pytest -q are not project checks here). Please align it with the issue acceptance criteria, keep the scope to CellFence's actual contributor workflow, and use relevant validation such as git diff --check, npm run build, npm test, or a focused node --test ... command.

[aoto-tech]

@Machumerre I updated this PR to address the requested changes. The contributor workflow now uses CellFence/npm validation commands instead of make test / pytest -q, removes trailing whitespace, clarifies targeted validation versus skipped slow checks, and the PR description now includes Fixes #27 plus a validation section. Validation: git diff --check origin/main...HEAD passed locally, and GitHub Actions completed successfully on the updated branch.

[aoto-tech]

Follow-up fixes landed and CI is green.

[aoto-tech]

@Machumerre I added one more follow-up after rebasing onto the latest main: the changed-check plugin cache test now freezes the trusted-input clock while asserting the seeded cache hit. This removes the minute-boundary flake seen in the Node 24 smoke job. Local build and targeted engine API coverage test passed, and the latest GitHub Actions run completed successfully.