Implement API versioning with /v1 URL prefix and backward compatibility

[nanaf6203-bit]

Area: API Standards
Priority: P1 — High

Description

Hard-coded v1 paths make future API evolution difficult. Without explicit versioning, breaking changes risk breaking integrations. Add /v1/ prefix to all endpoints with a clear versioning policy and migration plan for v2.

Acceptance Criteria

• Enable URI versioning: app.enableVersioning({ type: VersioningType.URI, defaultVersion: '1' }) in main.ts
• All endpoints accessible under /v1/... (current unversioned paths redirect or stay for backward compat)
• Update Swagger document to show /v1 paths in OpenAPI
• Update Swagger UI to allow version selector
• Add @Version('1') decorator on controllers for explicit documentation
• Document versioning policy in docs/API_VERSIONING.md (deprecation timeline, sunset headers)
• Tests: /v1/health and /health both return 200; v2 rejected with 404
• Add Sunset HTTP header support per RFC 8594

Technical Notes

• Deprecation policy: 6 months notice + 3 months grace before sunset
• Header approach: Deprecation + Sunset headers per RFC 8594

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[grantfox-oss]

🦊 GrantFox — @Menjay7 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #59)
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