Implement user registration form for new students

[aolguin89]

User Story

As a new student
I want to register an account
So that I can enroll in courses and take exams

Description

Create public registration form for students to create their own accounts.

Prerequisites

• User model and DAO already exist (completed)

Tasks

Servlet

• Create RegisterServlet.java in controller/ package
• Handle GET: display registration form
• Handle POST: process registration
• Validate input fields (required, format, uniqueness)
• Hash password with SHA2 before storing
• Set role to 'student' by default
• Set is_active to true
• Redirect to login page on success
• Configure servlet mapping (/register)

View

• Create register.jsp (public, not in WEB-INF)
• Use layout includes (header, footer, navbar)
• Registration form with fields:
  • Username (required, unique)
  • Email (required, unique)
  • Password (required, min 6 chars)
  • Confirm password (must match)
  • First name (required)
  • Last name (required)
  • DNI (optional)
  • Phone (optional)
  • Birth date (optional)
  • Gender (optional)
• Client-side validation (HTML5 + optional JavaScript)
• Display error messages for validation failures

Validation

• Username: 3-50 chars, alphanumeric + underscore only
• Email: valid email format, unique in database
• Password: minimum 6 characters
• Confirm password matches
• Check username and email uniqueness before insert
• Display field-specific error messages

Navbar Update

• Add "Register" link (only when not logged in)
• Show on login.jsp and index.jsp

Acceptance Criteria

• Registration form validates all inputs
• Duplicate username/email prevented with clear error
• Password confirmation works
• New user created with role 'student'
• Success: redirect to login with message
• Failure: show form with error messages (preserve valid fields)
• "Register" link visible to anonymous users only