Add Save/Create Account feature with login and registration pages

[jimeng999]

Implements: Issue #11 - Save/Create Account [$50 Bounty]

What was implemented:

1. Account Page (src/documents/account.html.eco)

   • Login form with email/password fields
   • Registration form with name, email, password confirmation
   • Client-side password validation
   • Session persistence via localStorage
   • Toggle between login/register views
   • Welcome back message for returning users

2. API Route Documentation (API_ROUTES_ACCOUNT.md)

   • POST /api/account/register - Create new user
   • POST /api/account/login - Authenticate user
   • GET /api/account/me - Get current user info
   • MongoDB integration example
   • LevelUP integration example
   • Security best practices

Design:

• Modeled after Stripe's clean login page design
• Semantic HTML5 form structure
• Accessible form labels and placeholders
• Client-side validation before submission
• Session memory using localStorage

References:

• Issue: Save/Create Account [$50] #11
• Stripe login: https://manage.stripe.com/login
• Mozilla Persona docs: https://developer.mozilla.org/en-US/Persona

Fixes #11