Add how-to for debugging blocks with the native `zesu` binary

[bgravenorst]

Summary

The native zesu binary is the practical reference for two debugging workflows:

• zkVM integrators validating their wiring by comparing their guest's 41-byte commitment to the native binary's commitment for the same input.
• Operators reproducing a failing block locally during incident response, without involving any zkVM.

The docs don't currently cover either workflow. This issue asks for a how-to that does.

Suggested scope

• How to obtain a block bundle to test against: capture one from an execution client, use one of the canonical fixtures, or generate one with the available tooling.
• Running the native zesu binary against that input.
• Comparing the 41-byte commitment against an expected value, or against the commitment a zkVM integration produces for the same input.
• Interpreting a divergence — what it does and doesn't tell you about where the bug lives.

Out of scope

• How to capture witnesses from a specific execution client. Witness production is covered in docs/concepts/witness-retrieval.mdx; this page should reference it rather than duplicate it.
• The full zkVM integration flow. That belongs in the integrator content elsewhere.
• Architecture of the native binary internals. Zesu is currently alpha and a fast-moving target — documentation should stay focused on user-facing usage rather than implementation details.

Notes

• Suggested location: how-to/debug-with-native-binary.mdx or similar. Writer should pick the page name that fits the docs IA.
• Lands cleanly after the install issue (Document how to install and build the native zesu binary #20) is merged so this page can link to install steps rather than restate them.
• The wire-format additions tracked in docs/concepts/inputs-and-outputs.mdx: missing wire formats and design rationale #18 will give this page a canonical place to link for input-format details.
• Zesu is in alpha. Documentation should reflect that behaviours may change.