fix: reject empty default project resolution

[ashishmax31]

Summary

• select only projects with non-empty names
• fall back to organization projects when the current-user response is empty or malformed
• return a clear error when neither endpoint yields a usable project
• add regression coverage for the Hub membership-object response shape

Testing

• go test ./...
• go vet ./...

Addresses the CLI robustness portion of #7. The Hub API contract mismatch remains a server-side concern.