Add UI settings API and improve context initialization

- Add /settings/ui GET and PUT endpoints for UI settings
- Improve ThemeContext with better initialization and auto accent handling
- Update SidebarContext with expanded state persistence
- Fix context initialization in ModulesContext and ViewModeContext
- Update components to use improved theme/sidebar contexts

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/Login.tsx

@@ -13,7 +13,7 @@ export default function Login() {
   const [email, setEmail] = useState('');
   const [isRegister, setIsRegister] = useState(false);
   const [error, setError] = useState('');
-  const [registrationEnabled, setRegistrationEnabled] = useState(true);
+  const [registrationEnabled, setRegistrationEnabled] = useState<boolean | null>(null);
   const { login, register } = useAuth();
   const { t, language, setLanguage } = useTranslation();
   const { theme, toggleTheme, showDarkModeLogin, showLanguageLogin, showDarkModeToggle, showLanguageToggle } = useTheme();
@@ -22,23 +22,31 @@ export default function Login() {
 
   // Check if registration is enabled
   useEffect(() => {
+    let isMounted = true;
     const checkRegistrationStatus = async () => {
       try {
         const response = await fetch('/api/v1/auth/registration-status');
         if (response.ok) {
           const data = await response.json();
-          setRegistrationEnabled(data.registration_enabled !== false);
+          const enabled = data.registration_enabled === true;
+          if (isMounted) {
+            setRegistrationEnabled(enabled);
+            if (!enabled) setIsRegister(false);
+          }
         } else {
           // Default to enabled if we can't fetch the setting
-          setRegistrationEnabled(true);
+          if (isMounted) setRegistrationEnabled(true);
         }
       } catch (error) {
         // Default to enabled if we can't fetch the setting
-        setRegistrationEnabled(true);
+        if (isMounted) setRegistrationEnabled(true);
       }
     };
 
     checkRegistrationStatus();
+    return () => {
+      isMounted = false;
+    };
   }, []);
 
   const handleSubmit = async (e: FormEvent) => {
@@ -129,7 +137,7 @@ export default function Login() {
         </form>
 
         <div className="login-footer">
-          {registrationEnabled && (
+          {registrationEnabled === true && (
             <button
               onClick={() => {
                 setIsRegister(!isRegister);

frontend/src/pages/admin/Features.tsx

@@ -13,7 +13,7 @@ export default function Features() {
     const { user: currentUser } = useAuth();
     const { t } = useTranslation();
     const { toggleMobileMenu } = useSidebar();
-    const { moduleStates, setModuleEnabled, saveModulesToBackend, hasInitialized } = useModules();
+    const { moduleStates, setModuleEnabled, saveModulesToBackend, hasInitialized, isLoading } = useModules();
     const [activeTab, setActiveTab] = useState<TabId>('feature1');
     const hasUserMadeChanges = useRef(false);
     const saveRef = useRef(saveModulesToBackend);
@@ -119,6 +119,9 @@ export default function Features() {
     };
 
     const renderTabContent = () => {
+        if (!hasInitialized || isLoading) {
+            return <div className="loading">Loading...</div>;
+        }
         switch (activeTab) {
             case 'feature1':
                 return (