[Editor] Add a file explorer and workspace tree

[Atharv777]

Summary

Add a sidebar file explorer for navigating project structure.

Why this matters

Projects need visible structure. Without it, the IDE feels incomplete.

Scope

• Tree view for files/folders
• Expand/collapse folders
• Open files from explorer

Acceptance Criteria

• Users can browse project structure
• Files open correctly
• Tree reflects real workspace state
• UI updates dynamically

Files Involved

• pages/app/index.jsx
• components/*
• server/project_routes.py

Difficulty

Medium

Labels: frontend editor enhancement