fix: prevent command injection in example URL opening

[maxisbey]

Summary

Fix a command injection issue in the example clients, mirroring the equivalent fix in the Python SDK (modelcontextprotocol/python-sdk#2082).

Problem

elicitationUrlExample.ts and simpleOAuthClient.ts used exec() with string interpolation to open URLs in the browser:

const command = `open "${url}"`;
exec(command, error => { ... });

exec() spawns a shell, so a crafted URL can break out of the quotes and execute arbitrary commands. The original code also hardcoded open, which only works on macOS.

Fix

• Replace exec/execFile with the open package, which handles cross-platform browser opening safely (macOS, Windows, Linux, WSL) without shell invocation
• Add URL scheme validation (allowlist: http:, https:) with proper try/catch around new URL()
• Remove unused child_process imports

The open package is added only to the examples/client package ("private": true, never published to npm), not to the SDK itself.

_{AI Disclaimer}

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