Multi-Window System

Description

Implement support for multiple windows, each with independent navigation state. Users can open multiple Explorer windows, media viewers, or settings panels.

Implementation Notes

• Each window has independent router state
• Tauri: use multi-window API
• Web: use browser windows or tabs
• Window state persists (size, position, route)
• Cross-window communication via events

Acceptance Criteria

• Open new Explorer window from menu
• Each window has independent navigation
• Window position/size persists
• Cross-window drag and drop
• Windows share library state
• Close all windows command
• Platform-specific window controls (traffic lights on macOS)