Prepare contributor readiness path for first external PR

[codeforester]

Problem

The 1.1.0 product review calls out the lack of external contributors as a remaining adoption and trust signal. Base has strong internal workflow documentation, but it needs an intentionally small contributor-readiness path that helps a new external contributor find, validate, and submit a safe first change.

Desired outcome

Create a practical first-external-PR path: clear starter issue criteria, contributor-facing validation commands, and a small set of issues that are safe for someone outside the maintainer loop.

Scope

• Review current CONTRIBUTING.md, docs/github-workflow.md, issue templates, and labels from an external contributor perspective.
• Define what qualifies as a good first Base contribution.
• Create or tag a small set of starter issues if the current backlog lacks good candidates.
• Make the local validation path easy to find for documentation-only, Bash, Python, and full-suite changes.
• Avoid exposing internal-only assumptions that a first-time contributor cannot satisfy.

Non-goals

• Do not loosen validation or review expectations just to make contribution easier.
• Do not add broad governance process before there are contributors.
• Do not create fake starter issues that do not provide real product value.

Acceptance criteria

• Contributor-facing docs explain how to choose a starter issue and validate a first PR.
• At least one real low-risk starter issue exists or is identified.
• The contribution path distinguishes docs-only checks from full Base validation.
• The issue label/project workflow remains consistent with Base-managed repo standards.