docs: add PeerDAS protocol overview

[perfogic]

Summary

This PR adds a dedicated PeerDAS documentation structure under the Protocol Wiki research section.

Changes include:

• Move the existing PeerDAS page into docs/wiki/research/peerdas/introduction.md.
• Add a new docs/wiki/research/peerdas/protocol-overview.md page explaining the high-level PeerDAS protocol flow.
• Update the Research sidebar so PeerDAS is a section with:
  • Introduction
  • Protocol Overview
• Update the existing EPF Study Group Week 6 PeerDAS link to the new introduction page path.

Motivation

The PeerDAS material was previously referenced from a weekly update (eth-protocol-fellows/cohort-seven#98). Based on review feedback, the protocol details are better suited as standalone Protocol Wiki documentation that can be linked from weekly progress updates.

This keeps weekly updates focused on progress while moving reusable protocol documentation into epf.wiki.

Testing

• Previewed locally with:

cd docs
python3 -m http.server 3001

• Checked local routes:
  • http://localhost:3001/#/wiki/research/peerdas/introduction
  • http://localhost:3001/#/wiki/research/peerdas/protocol-overview

[perfogic]

@taxmeifyoucan can you help me check this, thank you for your time 💯