[Backend] Amortization total due is understated by all interest

[ogazboiz]

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Description

The schedule total subtracts total interest rather than adding it, so the amount presented as due omits all interest.

Component: Backend
Location: backend/src/controllers/loanController.ts -> buildAmortizationSchedule
Severity: Critical

How to reproduce / find it

Build a schedule and compare total due against principal plus interest.

Expected behavior

Total due should be principal plus total interest.

Notes for contributors

This is a logic/behavior defect, not a compile error. Please open one PR per fix that references this issue and names the file and function above.

[Bilalishaq7]

Gooday maintainer,
I can fix this and i'd submit a PR shortly after assignment

[raizo07]

@raizo07 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, kindly assign this issue to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @raizo07 to this issue.

[Fash004]

@Fash004 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, I'd like to work on this issue.

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[extolkom]

@extolkom has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Please assign me

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