docs(aps): plan public contribution surface

[joshuaboys]

Summary

• add the Draft PUBDIR APS module with a public north star and product principles
• define contribution acceptance lanes, maintainer checkpoints, a curated roadmap, and contributor issue hygiene
• plan an opt-in, one-way APS-to-GitHub-Issues projection while keeping APS canonical
• register the module and its success criterion in the root APS index

Why

kindling is likely to receive more external attention. Prospective contributors need a concrete direction, clear boundaries on acceptable work, and a small set of genuinely ready opportunities rather than the entire internal APS tree.

Impact

Planning and documentation only. All seven PUBDIR work items remain Draft, so this PR does not authorise implementation or publish any contributor issues.

Validation

• aps lint plans — 11 files checked, no issues
• git diff --check
• pre-commit pnpm -r run type-check
• pre-commit oxfmt