Bump firewall to v0.27.42 and mcpg to v0.4.6

[lpcox]

Bump the pinned default versions of the AWF firewall and the MCP Gateway to their latest releases.

Changes

Update pkg/constants/version_constants.go:

• DefaultFirewallVersion: v0.27.41 → v0.27.42
• DefaultMCPGatewayVersion: v0.4.5 → v0.4.6

Releases

• Firewall: https://github.com/github/gh-aw-firewall/releases/tag/v0.27.42
• MCP Gateway: https://github.com/github/gh-aw-mcpg/releases/tag/v0.4.6

Follow-up

• Run make recompile to regenerate .lock.yml files with the new pinned versions.
• Update any golden/test fixtures that reference the old versions.