feat(charts): visualize contributor activity heatmap

[marcgc21]

Description

Create a heatmap chart that shows the number of commits per contributor per day. This offers a visual overview of how consistently each contributor is active over time, similar to GitHub’s contribution graph. Research if it is possible to get some graphic from github API

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📊 Chart Type

• Calendar-style heatmap (day-based grid)
• Rows per contributor (optional), columns per week/day

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🧾 Data Requirements

• Source: GitHub API (/repos/:owner/:repo/commits)
• Fields needed:
  • Commit date
  • Commit author

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✅ Tasks

• Fetch all commits with timestamps and authors
• Group by contributor and by day
• Generate a calendar heatmap (or small multiples per contributor)
• Use color intensity to indicate commit volume
• Include tooltip with exact counts per day

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📅 Example Output

Grid: 1 cell per day
Color intensity: Number of commits
Optional: Separate heatmaps per contributor

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✅ Acceptance Criteria

• Daily commit frequency visualized
• Color scale accurately reflects commit volume
• Tooltip or labels show commit counts
• (Optional) Filter or paginate per contributor
• Chart is responsive or downloadable