Bump firewall container to v0.27.39 and MCP gateway to v0.4.4

[lpcox]

Bump the default container versions to the latest releases.

Changes

• Firewall (AWF): v0.27.38 → v0.27.39 (release)
• MCP Gateway (mcpg): v0.4.3 → v0.4.4 (release)

Where

Update the defaults in pkg/constants/version_constants.go:

• DefaultFirewallVersion → v0.27.39
• DefaultMCPGatewayVersion → v0.4.4

Follow-up

• Run make recompile to regenerate .lock.yml files with the new pinned versions.
• Run make fmt and the relevant unit tests.
• Review the release notes for both bumps to check for any behavioral changes or new min-version constants that should be wired in.

[copilot-swe-agent]

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