Replace client h3 headings with McpClient component

Introduces a reusable `McpClient` component that provides consistent
styling, anchor links for navigation, and keeps client names out of the
site search index.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: jonathanhefner