[Editor] Add Monaco editor with multi-file project support

[Atharv777]

Summary

Integrate Monaco editor and support multiple files.

Why this matters

A real IDE needs a full-featured editor, not just chat-based code display.

Scope

• Integrate Monaco editor
• Multi-file tabs
• Syntax highlighting for Rust
• Track unsaved changes

Acceptance Criteria

• Multiple files can be opened
• Editor supports syntax highlighting
• Changes are tracked properly
• UI feels stable and responsive

Files Involved

• pages/app/index.jsx
• components/*
• package.json
• next.config.js

Difficulty

Hard

Labels: frontend editor enhancement