docs: add Dogwood block propagation design and specification

[evan-forbes]

Motivation

Document Dogwood for protocol review before implementation. The proposal targets low-latency block propagation from unpredictable proof-of-work entry points.

Solution

• Add the human-oriented design to docs/design/dogwood.md.
• Add the normative draft specification to docs/specs/dogwood.md.
• Preserve the reviewed documents and update their relative links for the repository layout.

The proposal covers selective portion subscriptions, proposer-specific routing, shared connection budgets, systematic Reed–Solomon coding with incremental decoding, message protections, and headerchain integration. This PR changes no runtime code.

Testing

• Verified that both documents match the source drafts apart from link updates.
• Checked local file links, heading anchors, Markdown fences, and trailing whitespace.
• Parsed the sequence diagram with Mermaid 8.13.10.
• Ran git diff --cached --check and ./scripts/changelog.py check.

No protocol implementation, controller simulation, or codec performance benchmark is included.

Changelog

No fragment is required because this PR changes only documentation.

Specifications & References

The documents link to the protocol research and relevant Zakura source files.

Follow-up Work

Resolve the remaining chain-binding and wire-profile choices. Implement and test the protocol. Measure controller behavior and codec latency before making performance claims.

[evan-forbes]

I'm not planning on adding all the the documents here, just wanted to show our work for now

the interesting thing is that I'm not sure we actually solved DOG's main issues, but I'm not sure DOG did now either after this.

Literally just subscribing to parts statically not inherently unlike gossip sub but different peers per part outperforms dynamic subscriptions!!!