[Docs] Gate contributions on explicit human intent

[hsliuustc0106]

Required human contributor answers

The human contributor explicitly supplied these answers for this rollout:

1. Outcome: Improve the quality of contributors' PRs.
2. Highest-leverage variable: PR quality, with clear thinking and results.
3. How this work moves it: Make this a hard constraint for a PR to be ready for review.
4. Customer and actual need: Every contributor; they need to think thoroughly about their PR.

Is a PR needed? Yes. The contributor explicitly requested separate repository PRs and updates to these PRs with mandatory template questions.

Bug-fix failure evidence: Not applicable; this is a contributor-workflow documentation change, not a runtime bug fix.

Why

Make contributor preparation explicitly establish the human's intended outcome and actual customer need before implementation or PR submission.

What

• Add four mandatory human-answer fields to the canonical PR template and require the contributor skill to verify completeness before submission. Preserve existing template sections; no CI workflow or server-side enforcement is added.
• Require explicit human answers for outcome, highest-leverage variable, how the work moves it rather than busywork, and customer/actual need.
• Reuse traceable answers, ask only for missing details, and wait; never manufacture human answers.
• Then ask whether a PR is needed at all; bug fixes require linked observed failure evidence.
• Link CONTRIBUTING to the canonical self-review gate; preserve existing checks and independent read-only reviews, automated review selection, and authorization boundaries.
• Existing PR [Docs] Review skills: merge-readiness gates and a readability focus #70 also touches self-review for merge-readiness checks; this change adds a separate intent section without duplicating that PR.

Validation

• git diff --check: passed for the prepared changes.
• Checked changed-file relative link targets, new anchors, and gate wording against the requested workflow.
• No runtime code changed; runtime/model/GPU tests not run for this documentation-only change. CI status is not claimed as passing.

Demo / evidence

N/A: contributor documentation and skill instructions only; no application behavior or performance claim.