docs: expand device management guide with comprehensive documentation (#17)

- Add device library section with search and filtering
- Document all device properties (basic, physical, appearance)
- Add device face placement explanation (front/rear/both)
- Document all 7 airflow direction types
- Add advanced device metadata section:
  - Network interfaces
  - Power ports (input) and outlets (output)
  - Device bays for blade chassis
  - Inventory items (RAM, CPU, etc.)
  - Part/serial numbers, asset tags, external links
- Add custom device creation workflow
- Document device images (bundled, custom, override per placement)
- Explain leapfrog movement behaviour
- Add collision detection documentation
- Document copy/duplicate and undo/redo operations

Fixes #4

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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: ggfevans