Add Win / Game Over Modal UI

[bhumishah2411]

Create reusable modal UI for win and game over states.

Acceptance Criteria:

• Semi-transparent overlay
• Centered modal box
• Show title and message
• Include buttons (Continue / New Game)
• Responsive layout

[kostpil]

Hello!! I would love to contribute in this issue. Can you assign it to me?

[unnati-09m]

Hi @bhumishah2411 , I'd like to work on this please assign it to me.