Fix mobile responsive layout issue #72

[Quantabhi]

This PR improves the mobile responsiveness of the Kanban board.

Changes

• Updated KanbanBoard.jsx to use flex-col on small screens and md:flex-row on larger screens.
• Updated Column.jsx to use w-full on mobile and md:w-56 on desktop.
• Improved the layout so Kanban columns stack vertically on mobile devices and display horizontally on larger screens.

Fixes #72

For the checklist:

✅ My code follows the project's style guidelines
✅ I tested my changes locally
⬜ I updated the README if my changes affect setup or usage
✅ My commit messages are clear and follow the conventional commit format

[anoopcodehack]

Thanks for the contribution!
I reviewed the changes, and the responsive layout improvements look good. Making the Kanban board stack vertically on mobile while keeping the horizontal layout on larger screens is a nice improvement.
I'll merge this PR shortly. Thanks for your contribution!