feat: add dark mode toggle with localStorage persistence

[vv-verse]

Closes #190

Description

Implemented a complete dark mode system with persistent theme support and responsive UI styling across major website sections.

Changes Made

• Added 🌙 / ☀️ dark mode toggle button in navbar
• Added dark mode styling for major sections and components
• Implemented theme switching using body.dark
• Added localStorage persistence for saved theme preference
• Automatically restores selected theme on page reload
• Improved UI readability and accessibility in low-light environments

UI Improvements

• Better nighttime browsing experience
• More modern and customizable interface
• Consistent dark styling across website sections
• Smooth and responsive theme switching behavior

Files Modified

• index.html
• css/style.css
• js/main.js

Features

• Persistent dark mode
• Responsive theme toggle
• Theme-aware cards, forms, filters, footer, and cart
• Dynamic navbar icon switching (🌙 / ☀️)

Type of Change

• Enhancement

Screenshots