fix: support Gmail OAuth refresh on Node 24

[CharGrnmn]

Summary

• restore full stored OAuth credentials and persist refreshed access tokens with mode 0600
• upgrade Google client libraries to versions compatible with Node 24.17 chunked token responses
• honor user-provided OAuth client keys ahead of the embedded fallback
• add native Node 22, Node 24.17, and current Node 24 OAuth regression coverage
• make releases explicit via gh release create so the release event can trigger npm publishing

Verification

• pnpm test:ci
• native OAuth regression test under Node 22 and Node 24.17
• live read-only Gmail profile and forced refresh under Node 24.17
• npm pack --dry-run --json
• workflow YAML parse