Support custom icons/images for plugins in marketplace

Feature Request

Allow plugin authors to specify custom icons/images for their plugins in the marketplace UI.

Current Behavior

All plugins display the same default placeholder icon in the Claude Code plugin marketplace UI, making it hard to visually distinguish between plugins.

Proposed Solution

Add an optional icon field to the plugin manifest (plugin.json) and/or marketplace entry schema, supporting either:

• A relative path to an image file (e.g., "icon": "./icon.png")
• A URL to a hosted image

Use Case

We maintain an internal company marketplace (fleek-plugin-marketplace) with 11 plugins (Analytics, Slack, Notion, Figma, Metabase, etc.). Users browse the catalog to install plugins individually, but they all look identical due to the default icon. Custom icons would greatly improve discoverability and UX.

Example

{
  "name": "slack",
  "description": "Slack integration via MCP",
  "icon": "./icon.png"
}