Sync github-agentic-workflows.instructions.md with v0.27.0 documentation

Synchronized instructions file with documentation changes from the new docs structure added in commit 1c80b2d.

### Changes Made

- Added new frontmatter fields: description, source, github-token, roles, strict, features, environment, container, services
- Added reaction and manual-approval fields to on: trigger configuration
- Added engine.env, engine.args, and engine.error_patterns configuration options
- Updated network permissions to include firewall configuration for Copilot engine (AWF support)
- Added search toolset to GitHub tools documentation
- Added recommendation to prefer toolset over allowed for GitHub tools configuration
- Updated engine network permissions section to reflect multi-engine support and AWF

### Documentation Commits Reviewed

- 1c80b2d Add shallow checkout to activation job for timestamp verification (#3013)

### Validation

- Followed prompting best practices (imperative mood, minimal examples)
- Maintained technical tone and brevity
- Updated only necessary sections
- Verified accuracy against current documentation
- Removed outdated content where applicable

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: github-actions[bot]