fix(docs): replace Math.random() nonce with crypto.randomUUID() in Wagmi setup example

[schoolkamsergj]

Summary

Replaces the insecure Math.random() nonce generation with crypto.randomUUID() in the Wagmi integration setup example.

Problem

Math.random() is not cryptographically secure and should never be used for SIWE (Sign-In With Ethereum) nonces. A predictable nonce can be exploited to perform replay attacks.

Before:

const clientNonce =
  Math.random().toString(36).substring(2, 15) +
  Math.random().toString(36).substring(2, 15);

After:

// Generate a cryptographically secure nonce using Web Crypto API
const clientNonce = crypto.randomUUID();

Why crypto.randomUUID()

• ✅ Cryptographically secure (uses the Web Crypto API)
• ✅ Available in all modern browsers and Node.js 14.17+
• ✅ Already used in the authenticate-users guide — keeps docs consistent
• ✅ Returns a UUID v4 — more than sufficient entropy for a SIWE nonce

Fixes #1390

[cb-heimdall]

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