fix: WalletConnect projectId silently falls back to 'demo' causing 403 errors

[dorukardahan]

Summary

Example 01's providers.tsx uses projectId: process.env.NEXT_PUBLIC_WALLETCONNECT_PROJECT_ID || "demo". The "demo" fallback keeps the UI alive but produces Reown 403 errors in the browser console on every page load. Additionally, the README links to cloud.walletconnect.com which now redirects to Reown (cloud.reown.com).

Actual behavior

Browser console on first load:

[warn] [Reown Config] Failed to fetch remote project configuration. Using local/default values. Error: HTTP status code: 403

Expected behavior

Clear error message when WalletConnect project ID is not configured, and updated URL in README.

Proposed fix

1. Throw or log a clear warning when NEXT_PUBLIC_WALLETCONNECT_PROJECT_ID is missing
2. Update README link from cloud.walletconnect.com to cloud.reown.com