[antoinetoussaint-byte]

Closes #14.

Summary

• service-swift published only darwin_amd64, darwin_arm64, and linux_amd64 assets, so core's downloader 404s on arm64 Linux hosts (companion images, arm64 CI runners, arm64 K8s nodes) when it resolves service-swift_<version>_linux_arm64.tar.gz.
• The agent links its own tree-sitter grammar (CGO_ENABLED=1), so the new build needs the aarch64 cross-cgo toolchain — already shipped by the goreleaser-cross image the release runs under. This is a goreleaser-only change; no release-workflow change is required.
• The existing archives name_template emits {name}_{version}_{os}_{arch}.tar.gz, so the new linux_arm64 asset satisfies core's downloader contract with no archive change.

Test plan

• goreleaser check passes with the new linux-arm64 build stanza.
• After merge, cut a new release; verify the arm64 asset is published:

  gh release view v<version> --repo codefly-dev/service-swift --json assets \
    --jq '[.assets[].name | select(contains("linux_arm64"))]'
  

Note: cutting the release (tagging a new version) is a maintainer step outside this PR's diff.