feat(charts): visualize issue activity over time

[marcgc21]

Description

Create a chart that tracks the number of issues opened and closed over time. This provides insight into the team’s workload and responsiveness to reported problems or feature requests.

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📊 Chart Type

• Line chart or grouped bar chart
• Two series: "Opened" and "Closed" issues

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🧾 Data Requirements

• Source: GitHub API (/repos/:owner/:repo/issues)
• Fields needed:
  • Issue creation date
  • Closing date (if applicable)
  • Note: exclude pull requests if needed (pull_request field)

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✅ Tasks

• Fetch issue data and group by week
• Count issues opened and closed per week
• Create a chart with two series (Opened and Closed)
• Include axis labels and a legend
• (Optional) Add interactivity or filters by label/type

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📅 Example Output

X-axis: Week (e.g., 2025-W29)
Y-axis: Number of issues
Line/Bar 1: Opened
Line/Bar 2: Closed

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✅ Acceptance Criteria

• Weekly opened and closed issues are shown clearly
• Opened and closed series are visually distinct
• Chart supports empty weeks gracefully
• Responsive design or downloadable format supported