feat(pygal): implement box-basic (#501)

## Summary
Implements `box-basic` for **pygal** library.

**Parent Issue:** #204
**Sub-Issue:** #461
**Base Branch:** `plot/box-basic`
**Attempt:** 1/3

## Implementation
- `plots/pygal/box/box-basic/default.py`

## Details
- Uses `pygal.Box()` to create box-and-whisker plots
- Compares statistical distributions across 4 groups (A, B, C, D)
- Each group has 50 data points with different means and standard
deviations
- Output size: 4800 × 2700 px (16:9 aspect ratio)
- Custom styling using project color palette (#306998, #FFD43B, #DC2626,
#059669, #8B5CF6, #F97316)
- Shows quartiles, whiskers, and outliers for each group

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>

Author: claude[bot]

plots/pygal/box/box-basic/default.py

@@ -33,7 +33,7 @@
 chart = pygal.Box(
     width=4800,
     height=2700,
-    title="Basic Box Plot",
+    title="Distribution Comparison by Group",
     x_title="Group",
     y_title="Value",
     style=custom_style,