Bump AWF firewall to v0.25.56 and MCP Gateway to v0.3.20

[lpcox]

Summary

Bump the Agent Workflow Firewall (AWF) and MCP Gateway to their latest releases.

Versions

Component	Current	Target
AWF Firewall	—	v0.25.56
MCP Gateway	—	v0.3.20

References

• Firewall release: https://github.com/github/gh-aw-firewall/releases/tag/v0.25.56
• MCP Gateway release: https://github.com/github/gh-aw-mcpg/releases/tag/v0.3.20