feat(bokeh): implement area-basic

[claude]

Summary

Implements area-basic for bokeh library.

Parent Issue: #99
Sub-Issue: #103
Attempt: 1/3

Implementation

• plots/bokeh/varea/area-basic/default.py

Details

• Uses varea glyph for filled area from baseline (0) to y values
• Adds line overlay on top for better visibility
• Supports customizable fill transparency (default: 0.5)
• Proper input validation with helpful error messages
• 16:9 aspect ratio (1600x900 pixels)
• Subtle grid styling (alpha=0.3)
• Includes sample data demo (monthly website traffic)

Quality Checklist

• Type hints on all parameters and return type
• Google-style docstring with Args, Returns, Raises, Example
• Input validation for empty data, missing columns, and alpha range
• Clear error messages with context
• Axes labeled with meaningful names
• Subtle grid (alpha=0.3)
• Semi-transparent fill (alpha=0.5)
• Line visible on top of fill area
• 16:9 aspect ratio
• Output saved as plot.png

[github-actions]

✅ Plot Tests Passed

Created with Python 3.14

Compatibility:

[codecov]

The author of this PR, claude[bot], is not an activated member of this organization on Codecov.
Please activate this user on Codecov to display this PR comment.
Coverage data is still being uploaded to Codecov.io for purposes of overall coverage calculations.
Please don't hesitate to email us at support@codecov.io with any questions.