Add MCP Apps hello world demo tool

Implements a simple MCP Apps tool that returns an interactive React UI:

- Add `mcp_apps_hello_world` tool with `_meta.ui/resourceUri` metadata
- Add resource handler for `ui://hello-world/app.html` returning HTML
- Create React app using `@modelcontextprotocol/ext-apps/react` hooks
- Add Vite build tooling to bundle React apps into single HTML files

The tool demonstrates the MCP Apps extension (SEP-1865) which allows
MCP servers to return interactive UI that runs in the client.

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

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

Author: jerome3o-anthropic