Add dark theme toggle

[muhduvais]

Summary

Add a dark theme toggle feature to the Helpore app, allowing users to switch between light and dark modes.

Motivation

• Improves accessibility and user comfort in low-light environments.
• Provides a modern and customizable user experience.
• Aligns with common UI/UX practices for web apps.

Requirements

• A toggle (switch or button) to enable/disable dark mode.
• There should have a smooth transition on toggle.
• Dark theme should apply across all pages and components.
• User preference should be remembered (e.g., using localStorage).
• Default theme can follow system preference (prefers-color-scheme).

Possible Implementation

• Use Tailwind CSS dark mode (class strategy).
• Add a global theme context/provider for React.
• Store user selection in localStorage.
• Apply theme class (dark) to the html or body element.

Acceptance Criteria

• User can toggle between light and dark themes.
• Smooth transition on toggle
• Preference persists across reloads.
• Theme applies consistently across the entire app.

Priority

Medium – Enhances UX but not blocking core functionality.