refactor(auth): migrate login and setup flows to typed feature module

- Introduce a new feature-based auth module under src/components/auth with clear separation of concerns:\n  - context/AuthContext.tsx for session lifecycle, onboarding status checks, token persistence, and auth actions\n  - view/* components for loading, route guarding, form layout, input fields, and error display\n  - shared auth constants, utility helpers, and type aliases (no interfaces)\n- Convert login and setup UIs to TypeScript and keep form state local to each component for readability and component-level ownership\n- Add explicit API payload typing and safe JSON parsing helpers to improve resilience when backend responses are malformed or incomplete\n- Centralize error fallback handling for auth requests to reduce repeated logic

- Replace legacy auth entrypoints with the new feature module in app wiring:\n  - App now imports AuthProvider and ProtectedRoute from src/components/auth\n  - WebSocketContext, TaskMasterContext, and Onboarding now consume useAuth from the new typed auth context\n- Remove duplicated legacy auth screens (LoginForm.jsx, SetupForm.jsx, ProtectedRoute.jsx)\n- Keep backward compatibility by turning src/contexts/AuthContext.jsx into a thin re-export of the new provider/hook

Result: auth code now follows a feature/domain structure, is fully typed, easier to navigate, and cleaner to extend without touching unrelated UI areas.

src/components/Onboarding.jsx

@@ -3,7 +3,7 @@ import { ChevronRight, ChevronLeft, Check, GitBranch, User, Mail, LogIn, Externa
 import SessionProviderLogo from './llm-logo-provider/SessionProviderLogo';
 import LoginModal from './LoginModal';
 import { authenticatedFetch } from '../utils/api';
-import { useAuth } from '../contexts/AuthContext';
+import { useAuth } from './auth/context/AuthContext';
 import { IS_PLATFORM } from '../constants/config';
 
 const Onboarding = ({ onComplete }) => {