Add unit tests for chart-utils formatting and calculation helpers

[aruneshwisdm]

Summary

apps/web/lib/dashboard/chart-utils.ts contains many pure utility functions (currency formatting, date range calculation, growth rate, linear regression) that currently have no unit tests.

Functions to test (pick at least 5)

• formatChartCurrency(value, currency) — formats numbers with K/M suffixes
• formatFullCurrency(value, currency) — full currency formatting for tooltips
• formatPercentage(value, decimals) — percentage formatting
• formatCompactNumber(value) — compact number formatting (K/M)
• calculateGrowthRate(current, previous) — growth rate between two values
• calculateConversionRate(converted, total) — conversion rate calculation
• linearRegression(data) — simple linear regression (slope + intercept)
• generateForecast(historicalData, forecastPeriods, confidenceInterval) — forecast generation
• getStatusLabel(status) — status string to display label
• calculateTotal(counts) — sum of status counts

Files

• Source: apps/web/lib/dashboard/chart-utils.ts
• Test file to create: apps/web/__tests__/lib/dashboard/chart-utils.test.ts

Acceptance criteria

• At least 5 of the listed functions have tests covering normal cases and edge cases
• Edge cases tested: zero values, negative numbers, division by zero, empty arrays
• calculateGrowthRate tested with previous = 0 (should return 100 when current > 0)
• linearRegression tested with empty array (returns slope: 0, intercept: 0)
• All tests pass with pnpm vitest run

Getting started

These are all pure functions with no database or API dependencies, so no mocking is needed.

[nightcityblade]

Hi, I'd like to work on this. I'll submit a PR shortly.