feat(letsplot): implement box-basic

[claude]

Summary

Implements box-basic for letsplot library.

Parent Issue: #203
Sub-Issue: #269
Base Branch: plot/box-basic
Attempt: 1/3

Implementation

• plots/letsplot/boxplot/box-basic/default.py

Details

• Creates basic box-and-whisker plot comparing statistical distributions across 4 groups (A, B, C, D)
• Uses lets-plot's grammar of graphics syntax (ggplot2-style)
• Applies project color palette (#306998, #FFD43B, #DC2626, #059669)
• Outputs 4800 x 2700 px PNG (16:9 aspect ratio per style guide)
• Typography scaled appropriately for output dimensions

[github-actions]

✅ Plot Tests Passed

Python 3.13 (required): passed

Compatibility:

Note: Only Python 3.13 is required to pass. Python 3.12 is tested for compatibility.