ci: auto-close PRs from forks and document the policy in README (#166)

Author: khsrali

.github/workflows/close-fork-prs.yml

@@ -0,0 +1,41 @@
+name: Close fork PRs
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - reopened
+
+permissions:
+  pull-requests: write
+
+jobs:
+  close-fork-pr:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.head.repo.full_name != github.repository
+    steps:
+      - name: Comment and close
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const pr = context.payload.pull_request;
+            const issuesUrl = `https://github.com/${context.repo.owner}/${context.repo.repo}/issues/new`;
+            const body = [
+              `Hi @${pr.user.login}, thank you so much for taking the time to propose this change — we really appreciate the gesture! 🙏`,
+              ``,
+              `A small note on how we work here: this site is maintained directly by the AiiDA team, and we kindly ask the community to share suggestions via **[issues](${issuesUrl})** rather than pull requests. Whatever the change — a typo, a broken link, outdated content, a content tweak, a bigger design idea — please describe it in an issue and we'll take it from there. The "Contributing" section of the README explains the why.`,
+              ``,
+              `Closing this PR for now. Your commits are still on \`${pr.head.repo.full_name}:${pr.head.ref}\` if you'd like to link to them from an issue.`,
+            ].join("\n");
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: pr.number,
+              body,
+            });
+            await github.rest.pulls.update({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: pr.number,
+              state: "closed",
+            });

README.md

@@ -27,6 +27,12 @@ npm run preview
 
 The site is deployed to Cloudflare Pages.
 
+## Contributing
+
+Thanks for your interest in helping! This site is maintained directly by the AiiDA team, and we kindly ask the community to share feedback through [**issues**](https://github.com/aiidateam/aiida-website/issues/new) rather than pull requests. Whether it's a typo, a broken link, outdated content, or a content suggestion — please open an issue and we'll take care of the implementation. To keep the workflow consistent, PRs opened from forks are gently auto-closed with a comment pointing back here.
+
+Two reasons behind the policy: (1) the site benefits from a single editorial voice, so changes flow through the team rather than landing piecemeal; and (2) Cloudflare Pages doesn't build preview deployments for fork PRs (a security default — the build environment can hold project secrets), so a fork PR can't be reviewed visually anyway. Routing through issues keeps the loop short for everyone.
+
 ## How to cite AiiDA
 
 If AiiDA helped your research, please cite the relevant papers below.