Bump MCP Gateway (mcpg) to v0.3.25

[lpcox]

Summary

Bump the MCP Gateway dependency from v0.3.23 to v0.3.25.

Changes needed

Update pkg/constants/version_constants.go:

const DefaultMCPGatewayVersion Version = "v0.3.25"

Release notes

See: https://github.com/github/gh-aw-mcpg/releases/tag/v0.3.25

Checklist

• Update DefaultMCPGatewayVersion in pkg/constants/version_constants.go
• Run make recompile to update lock files referencing the gateway image
• Verify smoke tests pass with new gateway version