Align `investment/portfolio` Module — Isolate Guards, DTOs, and Error Handling

[grantfox-oss]

Description
The portfolio module (src/investment/portfolio/) is the most complex domain module with 7 entities, 6 services, 7 DTOs, algorithms, and ML models. However:

• It has its own guards/ directory that may duplicate or conflict with common/guard/.
• Error handling is not domain-specific — financial operations (rebalancing, optimization) should return structured error responses.
• The 7 entities are all registered globally in app.module.ts rather than being encapsulated via TypeOrmModule.forFeature() in PortfolioModule.

Direction

1. Audit src/investment/portfolio/guards/ — merge unique guard logic into common/guard/, then delete the local guards directory.
2. Add TypeOrmModule.forFeature([...entities]) to PortfolioModule and remove portfolio entities from the global app.module.ts entity list.
3. Create domain-specific exception classes (InsufficientBalanceException, OptimizationFailedException, etc.) in src/investment/portfolio/exceptions/.
4. Ensure all DTOs use class-validator decorators and are validated by the global ValidationPipe.

Definition of Done

• Portfolio module is self-contained: owns its entities, guards, and exceptions.
• No portfolio-specific entities in the global TypeORM config.

Acceptance Criteria

• PortfolioModule uses TypeOrmModule.forFeature() for all 7 portfolio entities
• Portfolio entities are removed from app.module.ts global entity list
• src/investment/portfolio/guards/ directory is removed; any unique logic moved to common/guard/
• At least 2 domain-specific exception classes exist and are used in portfolio services
• All portfolio DTOs have class-validator decorators
• npm run build succeeds
• Portfolio tests pass (test/portfolio/)

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[clintjeff2]

Hello, I have 6 years of experience working on tasks like this and handling similar challenges across backend, frontend, and smart-contract development. I have carefully read and fully understood the task requirements, and I am confident I can deliver a clean, efficient, and well-tested solution promptly. I always ensure high-quality implementation, maintainability, and adherence to best practices.

Pull request in 2 days.

[SheyeJDev]

Hi, Maintainer,

Can I work on this issue?

I have 3 years of solid experience in nestjs, nodejs, typeorm and pg.

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #10)
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