Zod implementation for Signup form

Description:

Implemented a complete Zod-based validation system for the Volunteer Signup form to ensure clean, accurate, and secure user inputs. This update standardizes how data is validated before sending it to the backend, reducing invalid entries, trimming unnecessary whitespace, and preventing malformed phone numbers, emails, and passwords.

Key improvements include:

• Name validation with trimming and character restrictions
• Phone number normalization with India-specific rules (+91)
• Strict email formatting
• Password strength enforcement
• Age validation
• Updated UI to display inline error messages clearly

This enhances data quality, prevents common user mistakes, and ensures better user experience and backend compatibility. Resolves #102 (closed)

Type of Change:

• Bug Fix
• Feature Development
• Documentation

Testing:

• Tested on desktop
• Tested on mobile
• Tested in different browsers

Screenshots (if applicable):