Set up CI/CD pipeline for arcanea-code releases

[frankxai]

Pipeline Requirements

• GitHub Actions: typecheck, lint, test on PR
• Multi-platform binary builds (darwin-arm64, darwin-x64, linux-arm64, linux-x64, windows-x64)
• npm publish workflow for arcanea-code package
• Install script: curl -fsSL https://arcanea.ai/install | sh
• Homebrew formula: brew install arcanea-code
• Release automation with changelog generation
• Nix flake verification

[frankxai]

Progress

Completed

• arcanea-code.yml — GitHub Action triggered by /arc or /arcanea comments
• upstream-sync.yml — Weekly automated upstream sync check
• install script fully rebranded (arcanea-code binary, frankxai releases)
• build.ts — binary output name, user-agent header
• Existing typecheck.yml and test.yml work as-is

Remaining

• Multi-platform binary builds (needs npm org setup)
• npm publish workflow
• Homebrew formula
• Release automation with changelog