fix: support combined account filter in weekly summary endpoint (#2421)

[shauryavardhan1307]

Summary

This PR resolves a 404 Account not found error returned by /api/metrics/weekly-summary?accountId=combined by implementing support for the "combined" account filter. The endpoint now aggregates commits, PRs, active days, streaks, and top repository statistics across all of the user's linked GitHub/external accounts.

Closes #2421

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Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that changes existing behavior)
• 📝 Documentation update
• ♻️ Refactor / code cleanup (no functional change)
• ⚡ Performance improvement
• 🔒 Security fix
• 🧪 Tests only

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What Changed

• Weekly Summary Route Refactoring (route.ts):
  • Added support for accountId === "combined".
  • Extracted single-account weekly summary logic into a private helper function fetchWeeklySummaryForAccount.
  • Fetches weekly summaries for all linked accounts concurrently using Promise.allSettled.
  • Merges commits, PRs, and active days (capping the weekly active days at 7).
  • Uses the maximum current streak across accounts as a safe fallback.
  • Resolves the top repository by selecting the hottest repo from the account with the most commits.
• Unit Testing (weekly-summary-combined.test.ts):
  • Added a new unit test suite validating the concurrent fetching, merge logic, active days capping, and fallback rules.

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How to Test

1. Check out the branch fix/weekly-summary-combined-2421.
2. Run the new unit test suite to verify the endpoint's behavior with multiple accounts:

   npx vitest run test/weekly-summary-combined.test.ts

3. Load the dashboard in a browser using an account with multiple linked profiles, select the Combined view, and verify that the Weekly Summary widget successfully loads and displays aggregated stats instead of showing an error.

Expected result:

• The unit test passes successfully.
• The Weekly Summary widget fetches and aggregates statistics correctly for the combined account filter without returning a 404.

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Screenshots / Recordings

No UI changes; this PR only updates backend route logic.

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Checklist

• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console.log, debug code, or commented-out blocks
• Added or updated tests where applicable

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Accessibility (UI changes only)

Not applicable (Backend-only change).

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Additional Context

• The combined metrics cache uses a specific key (metrics:user-id:weekly-summary:{"accountId":"combined"}) to prevent collisions with individual account caches, while still utilizing cached data for each sub-account fetch.

[github-actions]

GSSoC Label Checklist 🏷️

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[shauryavardhan1307]

Hi @Priyanshu-byte-coder,I have updated the PR to resolve the type-check and build failures:

• TypeScript Fix: Added non-null assertion checks to session variables in src/app/api/metrics/weekly-summary/route.ts to satisfy strict typing for the getAllAccounts helper. Local type check (npm run type-check) is now passing successfully.
  Regarding the failing Playwright Smoke Tests and Visual Regression CI checks, these are pre-existing issues on the main branch. Since this PR is purely backend-focused (adding support for the combined filter on the weekly summary API route) and introduces no changes to UI components or layouts, it has no impact on these visual and UI regression suites.