#628 Add integration tests for portfolio balance aggregation

[vic-Gray]

Test that portfolio totals correctly aggregate deposits across multiple vaults.\n\nWhy: Incorrect balances are a critical user-facing bug.\n\nHints:\n- `backend/src/portfolio/portfolio.service.ts

[CNduka001]

@CNduka001 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi
I would take on this issue
ETA 4 hours

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[daveedAJ]

@daveedAJ has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hello team,

I’d love to work on this issue because accurate portfolio aggregation is essential for user trust and financial correctness. I have experience writing backend service tests and validating aggregation logic, and I’m confident I can add reliable coverage for multi-vault deposit calculations.

Thank you for considering me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @daveedAJ to this issue.