Add dark mode support to the Web UI

[ibnbd]

Description

The web UI currently only supports a light theme. Many developers prefer dark mode, especially when working late or in low-light environments.

Proposed Solution

• Add a theme toggle (light/dark/system) to the UI header or settings
• Use Tailwind CSS dark: variant classes
• Persist the preference in localStorage

Why This Matters

Dark mode is one of the most requested features in developer tools and significantly improves accessibility.

Getting Started

The frontend is in frontend/ and uses React 19 + Tailwind CSS 4. The entry point is frontend/src/App.tsx.

[ibnbd]

Dark mode is already supported — the UI follows your system preference via Tailwind CSS dark mode classes. Closing as completed.