- Centralize Claude CLI fingerprint constants (UA, x-stainless-*) in
pkg/claude with BuildCLI/CodeUserAgent helpers
- Reuse constants in DefaultHeaders, identity_service defaults, and
antigravity identity defaults to keep all callers in sync
- Extend ClaudeCodeValidator to accept both claude-cli/ and claude-code/
UA prefixes (transport/helper requests use the latter)
- Update related tests to cover the new UA prefix and version
d6df41feaa