fix(performance): replace loopback fetches with direct function calls to prevent serverless deadlocks

[VIDYANKSHINI]

Summary

This PR completely resolves the serverless function exhaustion issue (504 Gateway Timeouts) in the AI Insights route. The previous implementation erroneously made HTTP fetch() loopback calls to its own API endpoints, which quickly exhausts execution workers in serverless environments. The fix refactors /api/ai-insights/route.ts to directly invoke the underlying imported API handler modules (getContributions, getPrs, getStreak, getRepos) completely bypassing the network stack and redundant NextAuth session decryption.

Closes #

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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

• Refactored src/app/api/ai-insights/route.ts to remove 4 parallel fetch() calls hitting ${baseUrl}.
• Imported the GET route handlers directly from the respective metrics files (src/app/api/metrics/*/route.ts).
• Created a simulated NextRequest with the inherited Headers and Cookie to directly inject the authenticated session into the underlying handlers.
• Preserved existing JSON parsing flows without changing the response structure.

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How to Test

1. Load the developer dashboard locally.
2. Observe the AI Mentor widget fetching and summarizing metrics successfully.
3. Inspect network tools; there should no longer be an explosion of loopback calls originating from the server context targeting /api/metrics/....

Expected result: The AI Mentor dashboard continues to work identically, but the backend is significantly more resilient and returns responses faster with zero serverless deadlocks.

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