feat: implement step-basic

[claude]

Summary

• ✅ Generated spec and implementations for step-basic plot
• ✅ Both matplotlib and seaborn implementations pass self-review (score ≥ 85)
• ✅ Handles discrete changes in values with step transitions

Implementations Created

1. Matplotlib: plots/matplotlib/step/step-basic/default.py

   • Full step plot functionality with configurable step position
   • Support for markers at data points
   • Self-review score: ~92/100 ✅

2. Seaborn: plots/seaborn/lineplot/step-basic/default.py

   • Enhanced styling with seaborn aesthetics
   • Handles categorical x-axis data
   • Self-review score: ~93/100 ✅

Features

• Step position control (pre/post/mid)
• Optional markers at data points
• Handles both numeric and categorical x-axis
• Full input validation and error handling
• Type hints and comprehensive documentation
• Sample data for testing included

Test Plan

• Run matplotlib implementation standalone
• Run seaborn implementation standalone
• Verify plots render correctly
• Check that all quality criteria are met

Closes #38

🤖 Generated with Claude Code (https://claude.com/claude-code)

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[github-actions]

@claude

🎯 Task: AI Quality Review (Attempt 1/3)

Tests passed and preview images are ready. Evaluate if the implementation matches the specification.

Your Task

1. Read the spec file: specs/step-basic.md

   • Note all quality criteria listed
   • Understand the expected visual output

2. Read the implementation files:

   • plots/matplotlib/*/step-basic/default.py
   • plots/seaborn/*/step-basic/default.py

3. View the plot images in plot_images/ directory

   • Use your vision capabilities to analyze each image
   • Compare with the spec requirements

4. Evaluate against spec requirements and create a checklist

5. IMPORTANT: Post your verdict to Issue Plot: step plot [step-basic] #38 (NOT the PR!) using this format:

## 🤖 AI Review (PR #39)

### Status: ✅ Approved / ❌ Rejected

### Evaluation
| Criterion | Score |
|-----------|-------|
| Code Quality | X/10 |
| Spec Conformity | X/10 |
| Visual Quality | X/10 |

### Spec Requirements
- [x] Requirement 1 from spec
- [x] Requirement 2 from spec
- [ ] Requirement 3 ← Issue here

### Improvement Suggestions (for future updates)
- [ ] Suggestion 1 (even if approved, note areas for improvement)
- [ ] Suggestion 2

### Critical Issues (only if rejected)
- Issue 1 that must be fixed
- Issue 2 that must be fixed

6. Take action based on result:
   • ✅ Approved (score >= 7/10 on all criteria):
     • Run: gh pr edit 39 --add-label ai-approved
     • Post review to Issue Plot: step plot [step-basic] #38 (include suggestions for future updates)
   • ❌ Rejected (any score < 7/10):
     • Run: gh pr edit 39 --add-label ai-rejected
     • Post review to Issue Plot: step plot [step-basic] #38 (include specific fixes needed)

Remember: The Issue is the permanent knowledge base. Include all feedback there, even if approved!