feat: implement cr8 execution engine tasks

[Ishant5436]

Implements the cr8 subcommand group per the create protocol specification. Closes create-protocol/cr8#18.

• Adds matching the JSON in/out structure from the spec.
• Integration tests against local Anvil.
• Updated README with cr8 documentation linking to the spec.

[abhicris]

Welcome to kcolbchain, @Ishant5436 — glad you're here. 🌱

Here's what happens from this PR:

1. Our automated review looks for obvious issues (tests, secrets, size) within a couple of hours.
2. If it's clean and CI passes, we merge without back-and-forth.
3. If we need changes, we'll leave a specific comment — not a generic nit. Push another commit and we re-review.

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• Run the repo's tests locally (see the repo README.md).
• Keep the PR scoped to one concern — bigger PRs land slower.
• Don't commit tokens or .env contents.

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Thanks for writing the code. We're building this to last.

[abhicris]

🤖 Audit verdict: safe

Implementation is spec-driven with intentional mock data; real transactions only execute on localhost; no malicious code, credential leaks, supply chain attacks, or exploitable bugs detected.

Audited by the kcolbchain PR pipeline. See pipeline docs.