Feature/search bar UI

[Divyanshu227]

This pull request improves the user interface and accessibility of the search bar across the site, enhances dark mode styling, and refines the checkout logic for discounts and loyalty points. The most significant changes are grouped below.

UI and Accessibility Improvements:

• The search bar button in index.html, menu.html, orders.html, faq.html, and favorites.html now includes an accessible SVG search icon, replacing the empty button for better usability and visual clarity.
• The search bar's CSS (css/style.css) is updated for improved spacing, color, focus/hover states, and overall appearance, including a more visible placeholder and interactive button feedback.

Dark Mode Enhancements:

• Added comprehensive dark mode overrides for the search bar and its suggestions, ensuring colors and contrast are accessible and visually consistent in dark theme.
• Minor scrollbar styling improvements for dark mode.

Checkout and Discount Logic Improvements:

• Refactored the checkout logic in js/main.js to clearly separate coupon and points discounts, ensuring loyalty points are applied after coupons and both discounts are accurately reflected in the order summary.
  Theme Toggle Accessibility:

• Improved the dark mode toggle in js/main.js to initialize based on saved or OS preferences, update ARIA attributes for accessibility, and prevent duplicate event handlers.