feat: add utoipa OpenAPI spec and Swagger UI at /docs (Closes #30)

[ZacLou]

Closes #30

Changes

Adds OpenAPI 3.0 specification and Swagger UI to the WaveFlow API:

• Cargo.toml: Added utoipa v5 (with axum_extras) and utoipa-swagger-ui v9 dependencies
• mod.rs:
  • Added #[derive(OpenApi)] struct ApiDoc documenting all public endpoints and schemas
  • Merged SwaggerUi at /docs serving interactive API docs
  • OpenAPI JSON available at /api-docs/openapi.json

Documented endpoints

• GET /health — Health check
• GET /ready — Readiness check
• GET /api/v1/programs — List programs
• GET /api/v1/programs/:id — Get program details
• GET /api/v1/programs/:id/payouts — List program payouts
• GET /api/v1/programs/:id/contributors — List program contributors

Documented schemas

• ProgramRecord, ContributorRecord, PayoutRecord, ProgramStatus

Access Swagger UI at http://localhost:<port>/docs after startup.