Dark mode support via Tailwind 'class' strategy

[phertyameen]

Issue #8: Dark mode support via Tailwind 'class' strategy

Category: UI/Theming
Repo: bridgelet (frontend + docs)

Description

Add dark mode using Tailwind's darkMode: 'class' strategy. Persist preference in localStorage. Add a toggle button in the navbar. Ensure all pages and components are dark-mode tested.

Acceptance Criteria

• Implementation complete
• Tests passing
• Docs updated
• Reviewed and merged