feat: prevent race conditions during username registration

[ash1shkumar]

Summary

Implemented safer username registration handling to reduce race condition issues during concurrent signup requests.

Changes Made

• Added additional duplicate username verification before profile insertion
• Added fallback duplicate handling during profile creation
• Added automatic cleanup of partially created users on conflict
• Improved defensive error handling for concurrent registration requests

Security Improvements

• Reduced possibility of duplicate username creation during simultaneous signup attempts
• Added safer rollback handling for failed profile inserts

Testing

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

Issue

Closes #109

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 3:13pm