Refactor route helper boundaries

[haocn-ops]

Summary

• refactor V2 route boundaries by extracting shared responses, validation, billing routes, and domain repositories
• refactor admin and internal route helpers into shared response and validation modules
• refactor V1 system routes into shared response and validation helpers and add focused coverage

Included commits

• Refactor V2 route boundaries
• Refactor admin route helpers
• Refactor internal route helpers
• Refactor V1 system route helpers

Testing

• npm test