Add calculateSIP utility for rounded month-wise SIP projections

[Copilot]

This PR introduces a typed calculateSIP function in src/lib/calculators.ts to generate month-by-month SIP projections from monthly contribution, annual return rate, and tenure. It returns month, invested, returns, and gain per month, with all numeric outputs rounded via Math.round().

• New calculator module

  • Added src/lib/calculators.ts.
  • Exported SIPProjection interface and calculateSIP(...) function.

• SIP projection logic

  • Computes monthly projections for the full tenure (years * 12).
  • Uses standard SIP compounding (annuity-due form):
    M * (((1 + r)^n - 1) / r) * (1 + r).

• Output contract guarantees

  • Returns an array of { month, invested, returns, gain }.
  • Applies Math.round() to every returned numeric field.
  • Handles annualReturnRate = 0 without division by zero.

export function calculateSIP(
  monthlyAmount: number,
  annualReturnRate: number,
  years: number
): SIPProjection[] {
  // month-wise rounded SIP projections
}

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Project	Deployment	Actions	Updated (UTC)
fin-pal	Ready	Preview, Comment	May 25, 2026 9:12am