Add OpenAPI Documentation with Swagger

[Mkalbani]

Description

Integrate Swagger/OpenAPI documentation that is automatically generated from NestJS decorators and kept in sync with the codebase. Good API documentation accelerates frontend integration, onboarding of new contributors, and external audits of the security model. Every endpoint, DTO, and response schema should be fully documented and explorable in the Swagger UI.

Acceptance Criteria

• @nestjs/swagger is installed and a Swagger document is available at /api/docs
• All controllers use @ApiTags, @ApiOperation, and @ApiResponse decorators
• All DTOs use @ApiProperty with types, descriptions, and example values
• JWT auth is documented in Swagger with a bearer token input on the UI
• Error responses (400, 401, 403, 404, 429) are documented for every endpoint
• The Swagger UI is disabled in production via environment config
• An OpenAPI JSON export is available at /api/docs-json for tooling integration
• A CI check fails if any controller or DTO is missing required Swagger decorators

[Dickson2015]

The issue description is crystal clear. Maintainer I would love to work on this issue.

[grantfox-oss]

🦊 GrantFox — @Dickson2015 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #84)
2. Your PR will be reviewed by the MindFlowInteractive maintainers

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