Add PBKDF2 Password Hashing and Input Validation

[ranjitha1414]

1. Added PBKDF2 Password Hashing

• Implemented secure password hashing using PBKDF2WithHmacSHA256
• Added salt generation and secure hash verification
• Updated Person, Library, and login logic to use hashing instead of plain-text storage
• Modified the database schema to support longer hashed password fields
• Fixed an issue where passwords were being reset on application restart

2. Added Input Validation & Sanitization

• Created InputValidator class to enforce:
• character length limits required fields
• safe characters proper sanitization before database insertion
• Updated Library.java and Main.java to validate all user input before saving
• Prevented database crashes caused by oversized or invalid values