Create Portfolio REST API Endpoints

[grantfox-oss]

Description:
Implement REST API endpoints for portfolio management following OpenAPI/Swagger standards with proper error handling and response formats.

Acceptance Criteria:

• POST /api/portfolio - Create portfolio
• GET /api/portfolio/:id - Get portfolio
• GET /api/portfolio - List user portfolios
• PUT /api/portfolio/:id - Update portfolio
• DELETE /api/portfolio/:id - Archive portfolio
• Proper HTTP status codes (201, 200, 400, 404, 500)
• Standard error response format
• Input validation with DTO classes
• Swagger documentation auto-generated

Definition of Done:

• All endpoints implemented and tested
• Swagger documentation complete
• Error responses documented
• Can handle 100 requests/second per portfolio

Test Requirements:

• E2E tests for each endpoint
• Error scenario tests
• Load test

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[Kureszn]

I've reviewed the issue and believe I can contribute effectively. My experience spans software development, blockchain technologies, cybersecurity and open source collaboration. I take a structured approach to contributions carefully understanding the existing codebase, identifying the root cause and delivering a thoroughly tested implementation.

[Thirumurugan7]

I have vast experience with REST APIs.
Checkout my portfolio: 0xthiru.xyz

[grantfox-oss]

🦊 GrantFox — @Thirumurugan7 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 #324)
2. Your PR will be reviewed by the StellAIverse maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🦊 GrantFox — @Thirumurugan7 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 #324)
2. Your PR will be reviewed by the StellAIverse maintainers

Good luck! Track your progress on GrantFox.