doc(codeagent): support custom commands and subagents

[CarlJi]

No description provided.

[Copilot]

Pull Request Overview

This PR introduces support for custom commands and subagents to the CodeAgent system version 0.6. The changes aim to enhance AI code generation capabilities by implementing a structured command system inspired by Claude Code's design patterns.

Key changes:

• Added comprehensive documentation for custom command and subagent system design
• Updated GitHub workflow to handle additional event types (issues and PR review comments)
• Introduced template engine for GitHub context injection with standardized variable naming

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docs/codeagent-v0.6-design.md	Complete design documentation for v0.6 featuring custom commands, subagents, directory structure, and GitHub context injection
.github/workflows/claude.yml	Updated workflow triggers to support issues and pull request review comments

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@d8f640d). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #309   +/-   ##
=======================================
  Coverage        ?   13.10%           
=======================================
  Files           ?       25           
  Lines           ?     5427           
  Branches        ?        0           
=======================================
  Hits            ?      711           
  Misses          ?     4661           
  Partials        ?       55           

Flag	Coverage Δ
unittests	13.10% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.