Added custom 404 page, README improvements, and password visibility toggle

[deeksha31005-spec]

Added a custom 404 error page
Improved README formatting
Removed duplicate sections from README.md
Added show/hide password functionality in login page

Type of Contribution
Enhancement + Documentation + UI Improvement

Related Issue
Fixes #37

[deeksha31005-spec]

Hi @AditixAnand

I’m a GSSoC 2026 contributor and I have fixed the quiz scoring issue related to repeated option clicks.

Description

• Fixed the issue where users could increase the score multiple times by repeatedly clicking the same correct option
• Added logic to ensure each question is counted only once
• Improved quiz answer handling for better accuracy and fairness

Changes Made

• Added answeredQuestions array to track attempted questions
• Prevented duplicate score increments
• Updated quiz option selection logic in scripts/quiz.js

Type of Contribution
Bug Fix + Logic Improvement

Related Issue
Fixes #85