feat(highcharts): implement box-basic

Implements basic box plot for highcharts library following KISS style:
- Uses pandas for data preparation
- Calculates quartiles, whiskers, and outliers manually
- Uses color palette from style guide (#306998, #FFD43B, #059669, #8B5CF6)
- Includes outliers as separate scatter series
- Target dimensions: 4800x2700px
- Downloads Highcharts JS inline for headless Chrome compatibility

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Author: github-actions[bot]