Implement Client-Side and Server-Side Validation for All Forms

[andrew21-mch]

Add validation for all forms on the site to ensure that user inputs are accurate and secure. This includes both client-side validation (using JavaScript) and server-side validation (using PHP).

Steps to Complete:

Implement client-side validation using HTML5 attributes and JavaScript to provide immediate feedback.
Implement server-side validation in PHP to ensure data integrity and security before processing or storing input.

Acceptance Criteria:

All forms include both client-side and server-side validation.
Validation rules are enforced to prevent invalid or malicious data from being processed.