Add agentic workflow run information to step summary

[Copilot]

Updates the compiler to emit agentic workflow run information in the step summary as part of the step that writes aw_info.json. The step summary now includes a human-readable "## Agentic Run Information" section displaying the workflow metadata in JSON format.

What Changed

The generateCreateAwInfo function in pkg/workflow/compiler.go now adds the agentic workflow run information to the GitHub step summary using the core.summary API. This provides immediate visibility into workflow configuration and execution context directly in the GitHub Actions UI.

Example Output

When workflows run, the step summary will now display:

## Agentic Run Information

```json
{
  "engine_id": "claude",
  "engine_name": "Claude Code", 
  "model": "claude-3-5-sonnet-20241022",
  "version": "beta",
  "workflow_name": "Weekly Research",
  "experimental": false,
  "supports_tools_whitelist": true,
  "supports_http_transport": true,
  "run_id": 12345,
  "run_number": 42,
  "repository": "owner/repo",
  "ref": "refs/heads/main",
  "sha": "abc123",
  "actor": "username",
  "event_name": "workflow_dispatch",
  "staged": false,
  "created_at": "2024-01-15T10:30:00.000Z"
}

## Implementation Details

- Uses the same `core.summary` pattern established by other step summary generators in the codebase
- Maintains existing console logging while adding step summary output
- Properly formats JSON content in markdown code blocks for readability
- No breaking changes to existing functionality

## Testing

Added comprehensive test coverage with `TestStepSummaryIncludesAgenticRunInfo` to verify the step summary generation. All existing tests continue to pass.

> [!WARNING]
>
> <details>
> <summary>Firewall rules blocked me from connecting to one or more addresses (expand for details)</summary>
>
> #### I tried to connect to the following addresses, but was blocked by firewall rules:
>
> - `api.contoso.com`
>   - Triggering command: `/tmp/go-build3719727791/b279/cli.test -test.testlogfile=/tmp/go-build3719727791/b279/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true` (dns block)
>   - Triggering command: `/tmp/go-build704964953/b279/cli.test -test.testlogfile=/tmp/go-build704964953/b279/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true` (dns block)
>
> If you need me to access, download, or install something from one of these locations, you can either:
>
> - Configure [Actions setup steps](https://gh.io/copilot/actions-setup-steps) to set up my environment, which run before the firewall is enabled
> - Add the appropriate URLs or hosts to the custom allowlist in this repository's [Copilot coding agent settings](https://github.com/githubnext/gh-aw/settings/copilot/coding_agent) (admins only)
>
> </details>

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