feat: Add macOS-style window frame styling to code snippets

- Add window controls (red/yellow/green dots) header
- Darker background (#1e1e2e) with shadow
- app.ts filename display in header
- Better padding and typography for legibility

🤖 Generated with Claude Code (https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: michaeloboyle