Feature Request: Support Front + Back Views of a Rack

[GoodrichDev]

Summary
Add the ability to define both the front and back side of a rack, allowing devices mounted on the rear side to appear in the UI alongside front-mounted equipment.

Many real racks use rear-mounted devices:

• Patch panels
• Cable organizers
• PDUs
• Switches mounted backward
• Fiber shelves
• Rear-only appliances

Currently tinyDC visualizes only the front, which limits accuracy.

This could look like:

{
  "devices": [
    {
      "id": "pdu-back",
      "side": "back",
      "startU": 1,
      "heightU": 1
    }
  ]
}

UI could have buttons for [ Front ] [ Back ] or could display both front and back per rack.