Sync github-agentic-workflows.md with v0.33.11 (#7312)

Add missing frontmatter fields to instructions file based on schema analysis:
- sandbox: Sandbox configuration for AI engines
- labels: Workflow labels for categorization
- metadata: Custom metadata key-value pairs
- bots: Bot allowlist for triggering workflows
- safe-inputs: Custom lightweight MCP tools

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Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.5 <[email protected]>

Author: github-actions[bot]