[Feature]: Mobile Responsiveness for Monstr Workspace

[barunaniket]

What problem does this solve?

As a mobile user, I want to use the Monstr contest workspace on my phone/tablet so that I can write and submit code from anywhere.

Proposed solution

Optimize the split-pane workspace for mobile devices:

• Make the split pane vertical on mobile (stack problem statement above code editor)
• Ensure problem statement is readable on small screens
• Make code editor touch-friendly with proper keyboard handling
• Test on common device sizes (iPhone, iPad, Android)

Alternatives considered

• Disable Monstr on mobile (rejected - limits accessibility)
• Use a different UI layout only for mobile (accepted - implement stackable layout)

Difficulty: Intermediate