feat(charts): visualize code frequency over time

[marcgc21]

Description

Create a chart to display the evolution of the codebase over time, showing how many lines of code were added and deleted. This helps identify development intensity and periods of refactoring or large features.

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📊 Chart Type

• Stacked area chart (preferred)
• Alternatively, use a dual-line chart (one for additions, one for deletions)

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🧾 Data Requirements

• Source: GitHub API (/repos/:owner/:repo/stats/code_frequency)
• Fields needed:
  • Week timestamp
  • Lines added
  • Lines deleted

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✅ Tasks

• Fetch code frequency data from GitHub
• Process weekly totals of additions and deletions
• Implement stacked area chart (or dual-line chart)
• Add clear color distinction (e.g., green for additions, red for deletions)
• Include axis labels and a legend

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📅 Example Output

X-axis: Week (e.g., 2025-W28)
Y-axis: Number of lines
Areas/Lines: Additions (green), Deletions (red)

✅ Acceptance Criteria

• Clear visual distinction between added and deleted code
• Weekly granularity displayed accurately
• Labels and legend are present and readable
• Chart is responsive or exportable
• Graceful handling of weeks with no activity