Missing support for icon theme

[glen-84]

Icons have a theme property: https://modelcontextprotocol.io/specification/2025-11-25/schema#icon

This seems to be missing here:

• inspector/client/src/components/IconDisplay.tsx

  Lines 2 to 6 in 2b79e36

  	interface Icon {
  	src: string;
  	mimeType?: string;
  	sizes?: string[];
  	}

• inspector/client/src/components/PromptsTab.tsx

  Line 27 in 2b79e36

  icons?: { src: string; mimeType?: string; sizes?: string[] }[];

Very confusingly, the "History" output also omits this property, but I verified that it's being sent using Wireshark.