Redesign McpClient component as card and add supports prop

Redesign `McpClient` component to use a bordered card layout and add a
`supports` prop that displays supported MCP features in a standardized
header section. Migrate all client entries to use the new prop instead
of free-text `**Supports:**` lines in markdown.

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Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: jonathanhefner