refactor: improve insights composition workflow

[ash1shkumar]

📝 Description

This PR improves the insights generation architecture by introducing reusable composition helpers for analytics aggregation and summary preparation.

Previously, insight metrics and summary calculations were performed directly inside controller logic, creating tighter coupling between data orchestration and response generation. As reporting requirements expand, maintaining consistency across insight modules becomes increasingly difficult.

Changes Implemented

• Introduced reusable insight composition helpers
• Added buildOverviewMetrics() for overview analytics aggregation
• Added buildTaskSummary() for task insight summary generation
• Centralized derived metric calculations
• Reduced controller-level aggregation responsibilities
• Improved separation between data preparation and response composition
• Enhanced maintainability of the insights workflow

Benefits

• Cleaner analytics architecture
• Reduced coupling between controllers and aggregation logic
• Improved maintainability
• Better scalability for future reporting features
• Easier extension of insight generation workflows
• More consistent insight composition patterns across modules

🎯 Type of Change

• Refactoring
• Performance Improvement
• Code Quality Improvement

✅ Testing

• Verified overview insights API response remains unchanged
• Verified task insights API response remains unchanged
• Verified velocity calculations remain accurate
• Verified momentum calculations remain accurate
• Verified task summary generation remains accurate
• Verified heatmap generation remains functional
• Verified recent activity generation remains functional
• Verified contributor statistics continue to render correctly

Fixes #216

Expected Labels

level3 NSoC'26

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