Join Room button does not indicate valid room code

Problem
The Join Room button remains grey even after entering a valid room code.
This makes the UI unclear because users cannot easily see that the input is ready to submit.

Expected Behavior
When a user enters a room code:
The Join Room button should visually indicate it is ready to be clicked.
The button should change to a green/active state.

Current Behavior
The button stays in the default grey state even when a room code is entered.

Proposed Solution
Add conditional styling to the Join Room button based on the `roomCode` state.

Example:
Button becomes green when `roomCode.trim()` is not empty
Button remains grey when the input is empty

Possible Fix
Update the button class in `DebatePopup.tsx` using conditional styling based on `roomCode`.