Add gpai code commission page

[2digitsleft]

Adds the European Commission's official landing page for the GPAI Code of Practice to the "GPAI Code of Practice" subsection under "Official EU Sources".

What it is: The Commission's official page hosting the signatory list, the Signatory Form and signature process, the Vademecum, and Q&A about the Code. Distinct from the Code text itself (which is at code-of-practice.ai).

Why it belongs: It's the authoritative source for which providers have signed the Code and how to sign it — information not available on the Code text site. Complements the Code text entry without duplicating it.

Note: This PR depends on #12 being merged first. If PR #12 is rejected, please close this one too.

Checklist:

• Directly relevant to EU AI Act compliance
• Publicly accessible
• Working link
• Not already listed
• Description under 100 characters

[carloshvp]

Thanks for the follow-up PR. This Commission page is a useful complement to the Code text because it has the signatory list, signature process, Vademecum, and Q&A.

Two small things before merge:

1. This should land after Add: General-Purpose AI Code of Practice #12, since it builds on the new GPAI Code of Practice subsection.
2. The failing awesome-lint check is just the separator format. Please replace the em dashes with - in both entries:

- [General-Purpose AI Code of Practice](https://code-of-practice.ai/) - Voluntary tool for GPAI providers to demonstrate AI Act compliance on transparency, copyright, and safety.
- [GPAI Code of Practice (European Commission)](https://digital-strategy.ec.europa.eu/en/policies/contents-code-gpai) - Official Commission page with the GPAI Code of Practice signatory list, signature process, and Q&A.

Once #12 is merged and this branch is updated with the separator fix, I’ll take another look.

[carloshvp]

Thanks for the update @2digitsleft. The Commission page is a useful companion to the GPAI Code text, and the formatting now passes lint. I’m merging this now.