Create Portfolio REST API Endpoints

[SugaretaNajja]

Summary

This PR implements the Portfolio REST API endpoints for creating, retrieving, updating, listing, and archiving user portfolios.

The implementation follows the existing API conventions and OpenAPI/Swagger standards, with DTO-based input validation, consistent response formats, and proper HTTP status codes and error handling.

Changes Made

• Added POST /api/portfolio to create a portfolio.
• Added GET /api/portfolio/:id to retrieve a specific portfolio.
• Added GET /api/portfolio to list portfolios belonging to the user.
• Added PUT /api/portfolio/:id to update an existing portfolio.
• Added DELETE /api/portfolio/:id to archive a portfolio.
• Added DTOs for request validation.
• Implemented standardized error responses.
• Added appropriate HTTP status codes for success and failure scenarios.
• Added Swagger/OpenAPI documentation for all portfolio endpoints.
• Added E2E coverage for the portfolio API.
• Added tests for validation and error scenarios.
• Added load testing to verify the target of 100 requests/second per portfolio.

HTTP Status Codes

• 201 Created — Portfolio successfully created.
• 200 OK — Successful retrieval, update, or listing.
• 400 Bad Request — Invalid request or validation failure.
• 404 Not Found — Portfolio does not exist.
• 500 Internal Server Error — Unexpected server error.

Testing

• E2E tests for all portfolio endpoints.
• Validation and error scenario tests.
• Load testing against the required performance target.

Closes #324

[devIKargi]

@SugaretaNajja fix the CI please