feat: Add CRDT-powered real-time collaborative system design whiteboard (#1746)

[desireddymohithreddy0925]

Fixes #1746

Description

This PR introduces a real-time collaborative system design whiteboard. It solves the limitation of users having to leave PrepPilot to practice system design interviews with peers on external tools.

Changes Made

• Created SystemDesignWhiteboard.jsx in frontend/src/components/.
• Integrated yjs (CRDT) for lock-free, zero-latency state management.
• Integrated y-webrtc to synchronize canvas strokes directly peer-to-peer using WebRTC signaling.
• Built a custom React canvas integration that observes the shared Yjs array and re-renders strokes seamlessly.

Checklist

• Code compiles without errors
• Tested locally
• P2P functionality reduces server load compared to WebSocket relay servers

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📥 Commits

Reviewing files that changed from the base of the PR and between fd811d3 and 0177213.

⛔ Files ignored due to path filters (1)

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📒 Files selected for processing (2)

• frontend/package.json
• frontend/src/components/SystemDesignWhiteboard.jsx

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