docs: document CI release runbook

[cursor]

Summary

• Updated docs/development/release-checklist.md with a CI/release runbook for release-plz, cocogitto, cargo-nextest, cargo-deny, and cargo-machete.
• Added local reproduction commands, trigger conditions, and operational constraints verified against workflow/config files.
• Linked the release checklist from docs/INDEX.md so contributors can find the runbook.

Validation

• git diff --check HEAD~1..HEAD
• Local markdown link validation for docs/INDEX.md and docs/development/release-checklist.md

Codepaths covered

• .github/workflows/release-plz.yml
• .github/workflows/commitlint.yml
• .github/workflows/tests.yml
• .github/workflows/cargo-deny.yml
• .github/workflows/cargo-machete.yml
• release-plz.toml, cog.toml, cliff.toml, deny.toml, lefthook.yml

Knowledge gaps addressed

• Where CI/release automation is configured.
• Which events trigger each workflow.
• How to reproduce common CI failures locally.
• Constraints around per-crate tests, Kafka native dependencies, publishable crates, license/advisory policy, and unused dependency detection.