Add Codex metadata and Autotask eval docs

[rforgeon]

Summary

Adds Codex metadata for the Autotask plugin as a first representative cross-harness pattern for this marketplace.

What changed

• Add repo-level Codex marketplace metadata in .agents/plugins/marketplace.json
• Add .codex-plugin/plugin.json for msp-claude-plugins/kaseya/autotask
• Document the Codex install path in the README
• Add a small human-review eval set for Autotask ticket triage, time-entry drafting, and contract checks
• Document an optional Telvine publishing path with metadata-only telemetry guidance

Validation

jq . .agents/plugins/marketplace.json msp-claude-plugins/kaseya/autotask/.codex-plugin/plugin.json msp-claude-plugins/kaseya/autotask/.claude-plugin/plugin.json .claude-plugin/marketplace.json
git diff --cached --check

I also ran the Codex plugin validator against the Autotask plugin path. The new manifest parsed, but full validation is currently blocked by pre-existing empty name frontmatter in the billing, picklists, and ticket-notes-attachments skills.