State that contributions are dedicated under CC0

Adds a "Licence of contributions" section to CONTRIBUTING, a checkbox to
the pull request template, and a link from the README licence section.

Closes #148

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: TMHSDigital

.github/PULL_REQUEST_TEMPLATE.md

@@ -15,3 +15,4 @@
 - [ ] Stacks: followed `stacks/README.md`; no licence named in a stack's own words
 - [ ] `npm test && npm run validate` passes locally (CI runs the full `npm run check`, including the build)
 - [ ] If I publish the source, I say so above; if an agent or script drafted this, every licence fact was still read at the source by me
+- [ ] I dedicate this contribution to the public domain under CC0 1.0 (see CONTRIBUTING, "Licence of contributions")

CONTRIBUTING.md

@@ -105,6 +105,10 @@ A publisher who would rather not have their preview shown can open an issue; the
 
 Changes drafted with an agent or a script are judged on the diff like any other. Keep them small, keep tests in `site/checks.test.mjs` or `site/lib/lib.test.mjs` (a test file that `npm test` does not run is dropped), and name the issue the change fixes in the body (`Fixes #N`). A pull request that lists sources or licences the author did not read is closed: the catalog's one rule is that every licence fact was read at the source by the person who recorded it.
 
+## Licence of contributions
+
+By opening a pull request you dedicate your contribution to the public domain under [CC0 1.0](LICENSE), like the rest of the repository's metadata and documentation. Quotes from licence pages stay the publisher's words; they are used as short factual quotations, and the assets they describe keep their own licences.
+
 ## Research notes
 
 Local Gemini / deep-research drafts live under `RESEARCH/` as `R0N-<topic>.md` (gitignored; see [`docs/research-index.md`](docs/research-index.md)). Promote durable findings into catalog entries and `docs/` — don’t rely on drafts as the public source of truth.

README.md

@@ -398,4 +398,5 @@ If the catalog saves you time, you can [sponsor TMHSDigital on GitHub](https://g
 
 Catalog metadata and documentation in this repository are dedicated to the public domain
 under [CC0 1.0 Universal](LICENSE). Third-party assets linked from the catalog remain under
-their original licences. Verify terms on the source site before use.
+their original licences. Verify terms on the source site before use. Contributions are dedicated the same way; see
+[Licence of contributions](CONTRIBUTING.md#licence-of-contributions).