feat(ci): setup GitHub Action runners for building Node.js from source #224
Description
Problem
Some Node.js versions lack prebuilt binaries for certain platforms (particularly darwin-arm64). Even after probing for binaries directly, there may be versions where upstream simply doesn't provide prebuilt binaries.
Proposed Solution
Create a GitHub Actions workflow that can build Node.js from source for missing platform/version combinations and upload the resulting binaries to R2. This supplements the mirror with builds we control.
Scope
- Build Node.js from source on macOS (arm64, amd64) and Linux (arm64, amd64) runners
- Upload built binaries to R2 with proper metadata
- Trigger when gaps are detected in manifests after mirror sync
- Only build versions that are missing from specific platforms (not all versions)