[P2] Replace placeholder legal document endpoints with approved versioned content

[jjoonleo]

Problem

The document endpoints return placeholder Terms of Service, Privacy Policy, and service description strings.

Why this is not production ready

A real consumer service needs accurate legal documents, especially because this backend handles account data, social login, device tokens, Firebase push tokens, schedules, user notes, IP addresses, and API logs.

Evidence

• DocumentController.getTerms returns 이용약관 ~~~입니다.
• DocumentController.getPrivacyPolicy returns 개인정보처리방침 ~~~입니다.
• DocumentController.getOntimeDescription returns a hard-coded description string.

Required work

• Draft and approve real Terms of Service and Privacy Policy with legal/product stakeholders.
• Include data categories collected, purpose, retention, deletion, third-party providers, and user rights.
• Version documents and expose effective date/version in API responses.
• Decide whether document content belongs in code, database, CMS, or static files.
• Add tests ensuring endpoints return non-placeholder versioned content.

Acceptance criteria

• Terms and Privacy endpoints return approved, versioned, non-placeholder content.
• Privacy Policy covers OAuth providers, Firebase, tokens, schedules, notes, API logs, IP addresses, and deletion behavior.
• Document updates can be deployed/reviewed safely.