feat: add centralized API error handling utility

[ash1shkumar]

Summary

Implemented a centralized API error handling utility to reduce duplicated error handling logic across backend routes.

Changes Made

• Added reusable handleApiError() utility
• Centralized API error response formatting
• Replaced repeated catch-block logic in signup API
• Improved maintainability and cleaner backend structure

Benefits

• Consistent API error responses
• Easier debugging and logging
• Cleaner and more scalable route handlers
• Reduced duplicated backend code

Testing

• Verified successful production build using npm run build
• Confirmed TypeScript compilation passes without errors

Issue

Closes #110

Contributing Under

GSSoC 2026
NSoC 2026

Level 3 / Advanced

[vercel]

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[github-actions]

👋 Thank you for opening this pull request! I will review your changes and assist you soon.

[ash1shkumar]

@Shriii19 Please review this PR when possible. Since this implementation involves backend/security-focused improvements and production-level handling, could you please update the label from Level 2 to Level 3 / Advanced? Thanks!

[vercel]

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Project	Deployment	Actions	Updated (UTC)
flow-forge	Ready	Preview, Comment	May 25, 2026 3:27pm

[Shriii19]

@ash1shkumar resolve the conflicts.

[ash1shkumar]

@Shriii19 ,resolved conflicts. This PR is ready for review.