[SECURITY] Non-crypto random used for token generation fallback

[Livezt]

Security Bug: Non-Crypto Random in Token Fallback

File: src/web/client/GatewayBrowserClient.ts lines 230-237

Issue: Math.random() used as fallback for token generation. Predictable tokens.

Recommended Fix: Use crypto.getRandomValues() or crypto.randomUUID():

const token = crypto.getRandomValues(new Uint8Array(32));