docs: add Debugging & Logging section to AGENTS.md

[Copilot]

Agents had no documented path to enable targeted debug output from gh aw CLI runs, making it hard to diagnose issues without modifying source code.

Changes

• AGENTS.md — new "Debugging & Logging" section covering:
  • DEBUG=<pattern> and DEBUG_COLORS env vars with copy-paste examples
  • Namespace reference table (cli:*, workflow:*, parser:*, mcp:*, agentdrain:*, …)
  • How to discover a namespace (logger.New(...) at top of each .go file)
  • ACTIONS_RUNNER_DEBUG=true auto-activation in GitHub Actions debug runs
  • Output format: namespace message +elapsed

# Target a specific subsystem
DEBUG=cli:run_workflow_execution,cli:retry gh aw run workflow.md

# Capture full trace to file
DEBUG_COLORS=0 DEBUG=* gh aw compile workflow.md 2>debug.log

[Copilot]

Pull request overview

Adds targeted debugging and logging guidance for gh aw CLI runs.

Changes:

• Documents debug environment variables and namespace filters.
• Explains GitHub Actions debug behavior and log output format.

Show a summary per file

File	Description
AGENTS.md	Adds debugging and logging instructions for agents.

Review details

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• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Medium

[github-actions]

🎉 This pull request is included in a new release.

Release: v0.83.5