fix(onboarding): Change 'Go to Dashboard' to 'Go to Login'

The button after tenant creation was misleading - users need to log in first.
Changed button text and URL to explicitly point to /login.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/pages/TenantOnboardPage.tsx

@@ -659,12 +659,12 @@ const TenantOnboardPage: React.FC = () => {
 
               <button
                 onClick={() => {
-                  // Redirect to login or the business subdomain
-                  window.location.href = buildSubdomainUrl(formData.subdomain, '/');
+                  // Redirect to login on the business subdomain
+                  window.location.href = buildSubdomainUrl(formData.subdomain, '/login');
                 }}
                 className="px-8 py-3 bg-indigo-600 text-white rounded-lg hover:bg-indigo-700 font-medium"
               >
-                Go to Dashboard
+                Go to Login
               </button>
             </div>
           )}