feat: implement Contribution Forecast Engine (Phase 7)

[saidai-bhuvanesh]

Overview

This PR implements Phase 7: Contribution Forecast Engine to predict future contribution growth using linear regression and weekly velocity averages.

Key Changes

• ContributionForecast Component: Calculates average velocities, projects year-end total commits, and assigns consistency ratings.
• DashboardClient Integration: Positioned the forecast panel inside the Overview right aside layout.
• Tests: Created ContributionForecast.test.tsx to verify velocity calculations, trend directions, and zero-activity states.

Fixes #6213

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[github-actions]

🚨 Hey @saidai-bhuvanesh, the CI Pipeline is failing on this PR and it has been marked as status:blocked.

Please fix the issues before this can be reviewed. Here's how:

1. Run checks locally before pushing:

npm run format:check   # Check Prettier formatting
npm run lint           # Run ESLint
npm run typecheck      # TypeScript type check
npm run test           # Run unit tests (Vitest)
npm run build          # Verify production build passes

2. Auto-fix common issues:

npm run format         # Auto-fix formatting with Prettier
npm run lint -- --fix  # Auto-fix lint errors where possible

3. Check the full failure log here:
👉 View CI Run

Once you push a fix and the CI passes, the status:blocked label will be removed automatically. 💪

[Aamod-Dev]

Great work on the Contribution Forecast Engine component. The implementation in components/dashboard/ContributionForecast.test.tsx looks solid. However, this PR is blocked by a failing CI check. Please fix the typecheck and formatting issues so we can get this merged.