feat(auth): add input validation for registration and login using Zod

[Shreyanshi210205]

Description

Added Zod validation to ensure data integrity and type safety across the application.
The validation schemas are defined in a dedicated file/folder and applied at appropriate layers (API routes) to catch invalid inputs before processing.

Semver Changes

• Patch (bug fix, no new features)
• Minor (new features, no breaking changes)
• Major (breaking changes)

Issues

#40

Checklist

• I have read the Contributing Guidelines.