[Sirajmx]

Adds the Contribution Terms from legal, so contributions from non-members come with a patent license as well as the existing CC BY 3.0 copyright license. Members stay under the IAB Tech Lab IPR Policy, which controls on conflict.

This supersedes #136 and covers everything in it, plus the items below. #136 is left open for its author to close.

Changes

• CONTRIBUTING.md (replaced with the version supplied by legal)
  • Section 6 is now Contribution Terms (IPR): (a) copyright, (b) patents, (c) authority, (d) IAB Tech Lab members.
  • The contact for anyone who can't agree is agentic@iabtechlab.com. Add contribution terms with patent license (CONTRIBUTING, PR template, README) #136 had support@iabtechlab.com as an open item.
  • A pointer to the terms at the top, and a checkbox rule in section 4.
  • The #ipr anchor is unchanged, so existing links still resolve.
• .github/PULL_REQUEST_TEMPLATE.md: the closing licence line becomes a Contribution Terms checkbox. The existing template is kept rather than adding a second pull_request_template.md. The link is absolute because relative links don't resolve in a PR body.
• README.md: the submission paragraph now points to section 6 of CONTRIBUTING.md instead of stating its own copyright-only grant, so the two don't conflict.
• Issue forms: all four (change request, comment, editorial, implementation feedback) have a required checkbox agreeing to the Contribution Terms, including the patent license. The editorial form had none before.

For review

• The section 6 text is exactly as supplied.
• The only change from the supplied CONTRIBUTING.md is the note in section 2 ("Only issues and pull requests form the formal comment record…"). It stays a blockquote as on main, because the > markers were lost in transit.
• The other wording changes in sections 1–4 (dropped code formatting and dashes) are as supplied.

Checks

Run locally:

• Issue forms and labels.yml parse.
• Examples parse.
• scripts/check_appendix.py passes (69 fields).