Google social login has no credentials in production, so the "Continue with
Google" button (and its divider) errored on click. Gate the button + divider on
a new isGoogleConfigured() helper (requires GOOGLE_CLIENT_ID + GOOGLE_CLIENT_SECRET)
on both the login and signup pages, and guard the signInWithGoogle action as
defense in depth. The button reappears automatically once both env vars are set.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
