Feature/migrate pd blocks to curriculum

[Beloved1310]

What does this change?

This PR migrates a block currently pulled from the CYF-PD CMS (https://cyf-pd.netlify.app) into this repository so it can be maintained as a standard markdown block.

The CMS approach adds unnecessary complexity, is no longer actively used, and makes updates harder to test and review. By moving this content into common-content, contributors can improve it directly using existing workflows.

This PR:

• Migrates the markdown content of a PD block into common-content/en/blocks
• Updates the src reference in org-cyf-itp to point to the local block
• Removes the dependency on the external CYF-PD CMS for this content

This is part of a wider effort to migrate the remaining CYF-PD blocks used in org-cyf-itp (6 in total).

Common Content?

• Block/s

Common Theme?

• Yes

Issue number: #1745

Org Content?

Block Type

Checklist

• I have read the contributing guidelines
• I have checked my spelling and grammar with an automated tool
• I have previewed my changes to check the markdown renders as I intend
• I have run my code to check it works
• My changes follow our Style Guide

Who needs to know about this?

@illicitonion @cifarquhar