Add ink-mermaid to Useful Components

[mk668a]

Adds ink-mermaid to the Useful Components list.

• What it does: Renders Mermaid diagrams (flowchart, sequence, state, class, ER, XY chart) as ASCII/Unicode inside Ink-based terminal UIs.
• How: Thin wrapper around beautiful-mermaid — no headless browser, no external CLI, pure TypeScript.
• Status: Published on npm as ink-mermaid@0.1.0. MIT licensed. TypeScript types included. CI on Node 22/24.

import {Mermaid} from 'ink-mermaid';

<Mermaid code={`graph LR
  A[Start] --> B{Decision}
  B -->|Yes| C[Done]`} />