feat: add subagent orchestration kit

[Asheze1127]

Summary

• add a repo-local plugin entry for reusable sub-agent workflows
• add a subagent-orchestration-kit plugin with role definitions for idea consulting, coding, evaluation, review, and drift checking
• add HackHub-specific product context plus a portable project overview template for reuse in other repositories
• add usage documentation so the kit can be copied into other repos or used as prompt packs

Validation

• python3 -m json.tool .agents/plugins/marketplace.json
• python3 -m json.tool plugins/subagent-orchestration-kit/.codex-plugin/plugin.json

Notes

• this plugin packages reusable prompts and operating docs; it does not add new first-class agent types to Codex
• keeping this as a draft PR for manual review before anything lands on dev

[Asheze1127]

Superseded by #52. This earlier draft PR was based on unrelated local commits and should not be reviewed further.

[Asheze1127]

This draft was superseded because it included unrelated local commits. Please ignore #51 and review #52 instead.

[Asheze1127]

Subagent portability review has been applied on this branch.

Updated points:

• introduced contexts/project-overview.md as the canonical context file for reuse
• removed repo-specific URLs and placeholder contact metadata from the manifest
• added an MIT license file
• clarified marketplace merge guidance and reuse steps in the README
• aligned skill docs to the canonical context path

I will treat this PR as the review checkpoint for the plugin bundle and continue the product work on the separate opportunity/progress-checker-cycle-1 branch.