Implement Multi-Currency Expense Split Calculation and Preview Component

[Cjay-Cyber-2]

Description — what to implement and the why/impact.

Group expenses often involve different currencies or custom split ratios (percentage, shares, and exact amounts). This issue implements a robust expense split calculation engine and preview component so users can verify how much each participant owes before submitting the expense to the Stellar network.

Context & Requirements — background, constraints, design references, edge cases; grounded in the actual repo (real files, stack, conventions).

Calculations must be precise, avoiding floating-point rounding issues when splitting bills among multiple participants. The component should live in src/components/expenses/ and use Zustand (src/store/) or local React state to compute shares dynamically. All data structures must align with src/lib/types.ts.

Acceptance Criteria — a checklist ("- [ ] ...") of specific, testable conditions that define "done".

• Build a split calculation utility handling equal, exact, and percentage splits.
• Create ExpenseSplitPreview.tsx in src/components/expenses/ showing itemized participant breakdowns.
• Handle remainder distribution cleanly so split totals always match the exact expense amount.
• Ensure type safety with strict TypeScript and Zod validation.
• Pass npm run typecheck and npm test.

Implementation Guidance — likely files/modules to touch (use real paths from the repo context) and a suggested approach, without over-prescribing.

• Review utility patterns in src/lib/.
• Implement calculation helper functions with unit tests.
• Use Tailwind CSS classes consistent with the neobrutalist design system.

Testing & Validation — how the contributor should prove it works (tests to add/run, manual checks, screenshots for UI).

• Add unit tests covering various split combinations and edge cases (e.g., uneven division of pennies).
• Run npm test to verify test suite execution.

Submission Guidelines — must open a PR that includes "Closes #"; assignment is required before starting; follow the repo's existing style and conventions.

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Wave complexity: Medium

[Ranjeet2063]

Hi maintainers,

I would love to take this on. My planned approach:

• Build Implement Multi-Currency Expense Split Calculation and Preview Component with modular React/Next.js components, responsive styling, and proper loading/error states.
• Include component tests and verify clean production build with zero TypeScript/lint issues.

Happy to pick this up today—please assign to me!