docs: add ai contributing policy

[chaokunyang]

Why?

Apache Fory is aperformance-critical foundational serialization framework.
As AI-assisted contributions increase, we need a project policy that keeps review quality high, protects legal/provenance safety, and preserves long-term maintainability.

This policy is intended to:

• keep human accountability as the core rule
• reduce low-signal or unverified AI-generated changes
• require verifiable testing/performance evidence for sensitive paths
• align contribution practice with ASF legal and governance expectations

What does this PR do?

• Adds a new top-level policy document: AI_CONTRIBUTION_POLICY.md.
• Defines requirements for AI-assisted contributions, including:
  • contributor responsibility and line-by-line self review
  • privacy-safe disclosure expectations
  • verification requirements (tests/spec/perf evidence where applicable)
  • licensing/provenance requirements
  • quality gate and maintainer enforcement process
• Updates .github/pull_request_template.md to add an AI contribution checklist for PR authors.

Related issues

N/A

Does this PR introduce any user-facing change?

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?

Benchmark

N/A (documentation and PR template change only)

[pjfanning]

Can you mention license confirmation as a core principle?

[chaokunyang]

added a point:

• License/provenance confirmation: contributors MUST confirm submitted material is legally compatible and traceable, and MUST comply with ASF Generative Tooling Guidance.

[pandalee99]

How many lines of code, how large a change, or to what extent of AI involvement counts as substantial? It could be as simple as adding a single function, or just revising a short comment. Could we further define and clarify this specification?

[chaokunyang]

This is indeed ambiguous. I added some clarification:

Definition of substantial AI assistance:

• Substantial means AI materially influenced technical content, not only writing style.
• Contributors MUST mark AI assistance as substantial (yes) if any of the following apply:
  • AI generated or rewrote non-trivial code/test logic (even for a small change or a single function).
  • AI-generated or AI-refactored content is about 20 or more added/changed lines in aggregate.
  • AI materially influenced API, protocol, type mapping, performance, memory, or architecture decisions.
  • AI produced substantive technical text used in PR rationale (beyond grammar/translation cleanup).
• Contributors MAY mark substantial AI assistance as no for minor or narrow assistance only, such as spelling/grammar fixes, formatting, trivial comment wording edits, or other non-technical edits with no behavior impact.

Required disclosure fields:

• Whether substantial AI assistance was used (yes or no)
• Scope of assistance (for example: design drafting, code drafting, refactor suggestions, tests, docs)
• Affected files or subsystems (high-level)
• Human verification performed (checks run locally or in CI, and results reviewed by the contributor)
• Provenance and license confirmation (see Section 6)

Standard disclosure template (recommended):

AI Usage Disclosure
- substantial_ai_assistance: yes
- scope: <design drafting | code drafting | refactor suggestions | tests | docs | other>
- affected_files_or_subsystems: <high-level paths/modules>
- human_verification: <checks run locally or in CI + pass/fail summary + contributor reviewed results>
- performance_verification: <N/A or benchmark/regression evidence summary>
- provenance_license_confirmation: <Apache-2.0-compatible provenance confirmed; no incompatible third-party code introduced>