Remove awmg gateway binary and build infrastructure

[Copilot]

Removes the standalone awmg (Agentic Workflows MCP Gateway) binary, all associated build scripts, and documentation per requirements.

Changes

Source Code (~3,400 lines removed)

• Removed cmd/awmg/ - main binary entry point
• Removed pkg/awmg/ - gateway implementation and tests (gateway.go, 6 test files)
• Removed pkg/workflow/gateway*.go - step generation, validation, domain tests
• Removed sandbox.mcp configuration support from workflow compiler
• Cleaned up MCP gateway references in copilot_mcp.go, frontmatter_extraction_security.go, tools_parser.go

Build Infrastructure

• Removed install-awmg.sh installation script
• Removed awmg build targets from Makefile (build-awmg, platform-specific builds)
• Updated scripts/test-build-release.sh to remove awmg build validation
• Removed awmg binary patterns from .gitignore
• Removed awmg-specific lint exclusions from .golangci.yml

CI/CD

• Removed "AWMG Gateway Tests" matrix group from .github/workflows/ci.yml

Documentation (~2,500 lines removed)

• Removed docs/awmg.md, docs/mcp-gateway.md, specs/mcp-gateway.md
• Removed awmg references from DEVGUIDE.md, examples/README.md, specs/gosec.md, docs/src/content/docs/reference/sandbox.md
• Removed 4 example configuration files: examples/mcp-gateway-*.json

Notes

The MCPGatewayRuntimeConfig type and DefaultMCPGatewayPort constant remain in the codebase as they're referenced by existing configuration structures, but the feature itself is non-functional. Historical CHANGELOG entries preserved for reference.

Original prompt

Remove awmg gateway. Remove build scripts and go sources. Scan docs and remove as well.

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[pelikhan]

@copilot review changes, format, lint

[Copilot]

@copilot review changes, format, lint

All checks pass:

• ✅ Format: Code properly formatted
• ✅ Lint: 0 issues
• ✅ Code review: No issues found