icon request: Plate

### Describe the Icon

2 circles. One big, one small

### Links to Examples

_No response_

### Additional Information

_No response_

The issue names no file or test. Start by inspecting existing icon definitions and comparable two-circle icons, then confirm the intended visual for “Plate” with the issue author. Done means the new icon matches the project’s conventions and is included in the icon set.

索引モデルが issue の本文から書いたものです。