Use the agy CLI User-Agent family (antigravity/cli/{version} darwin/arm64)
on CPA macOS/arm64 hosts instead of the legacy hub-style antigravity/{version}
string. Resolve the cached version from the CLI auto-updater manifest
(darwin_arm64.json), then the GCS latest pointer, then antigravity-cli GCS
prefix listing, with fallback 1.0.8 when all sources fail.
Update AntigravityUserAgent helpers and executor default UA comment to match.
c296790801