📚 Note that needs triage and internal issues are closed

State in the contributing guide that issues under `needs triage` and
`internal` are not open to contributions. Every new issue starts under
`needs triage` until the product team reviews it, so contributors could
mistake a fresh issue for an invitation and send a PR that we then turn
down.

A PR opened on one of those issues may be closed without review,
without an explanation and without a reply. The wording follows the
existing note about AI-assisted content.

The help center page keeps its current wording for now.

AI-assisted-by: deepseek-v4.1-flash

CONTRIBUTING.md

@@ -67,6 +67,11 @@ If AI-assisted content is used, it must be carefully reviewed and verified by a
 Report bugs via [GitHub Issues](https://github.com/penpot/penpot/issues).
 Before filing, search existing issues to avoid duplicates.
 
+> **Note:** Every new issue starts under the `needs triage` label until the
+> product team reviews it. Issues under `needs triage` or `internal` are not
+> open to contributions — do not start work on them. Wait for a maintainer to
+> confirm it in the issue itself.
+
 Include the following when possible:
 
 1. Steps to reproduce the error.
@@ -164,10 +169,15 @@ To save time on both sides, please avoid submitting PRs that:
 - Submit AI-generated code without human review.
 - Skip local syntax and formatting checks before submitting.
 - Skip the [discussion step](#workflow) for non-bug-fix changes.
+- Open a PR for an issue under `needs triage` or `internal`. We may close
+  these PRs without review, without an explanation and without a reply.
 
 ### Good first issues
 
 We use the `good first issue` label to mark issues appropriate for newcomers.
+An issue is open to contributions only after a maintainer says so in the issue
+itself. Issues under `needs triage` or `internal` stay closed, however simple
+they look.
 
 ## Commit Guidelines