fix(auth): resolve demo login redirect loop, fix backend API bugs, restore clean login UI, and add comprehensive API docs with headers

src/app/dashboard/layout.tsx

@@ -20,7 +20,7 @@ export default function DashboardLayout({ children }: { children: ReactNode }) {
   const [dropdownOpen, setDropdownOpen] = useState(false)
   const dropdownRef = useRef<HTMLDivElement>(null)
   
-  const { userId, user, globalSettings, switchUser, hasAccessTo, loading } = useActiveUser();
+  const { userId, user, globalSettings, switchUser, logout, hasAccessTo, loading } = useActiveUser();
   const [maintenance, setMaintenance] = useState(false);
   const [checkingMaintenance, setCheckingMaintenance] = useState(true);
 
@@ -264,6 +264,13 @@ export default function DashboardLayout({ children }: { children: ReactNode }) {
                   >
                     Reset Demo
                   </button>
+                  <div className="h-px bg-border my-1" />
+                  <button 
+                    onClick={logout}
+                    className="w-full text-left flex items-center gap-2 px-3 py-2 text-sm text-red-500 hover:bg-red-500/10 rounded-lg transition-colors font-semibold"
+                  >
+                    Sign Out
+                  </button>
                 </div>
               </div>
             )}