[Task]: Quick Copy & Export Shortcuts

### Summary

Introduce keyboard shortcuts for fast copy/export actions.

### Milestone

1.6.0 — Power-User Features

### Details

_No response_

### Checklist

- [ ] ⌘C = Copy CSS
- [ ] ⌘⇧C = Copy SwiftUI
- [ ] ⌘E = Export PNG/SVG

### Priority

Low