feat(frontend): Implement complete authentication system

Implemented comprehensive JWT-based authentication with token refresh mechanism, user state management, and protected routes.

Changes:
- Upgraded API client from fetch to Axios with automatic token refresh interceptors
- Created API configuration with centralized endpoint definitions
- Implemented Zustand auth store for user state management with persistence
- Created React Query hooks for login, register, logout, and current user
- Built login and registration pages with form validation (Zod + React Hook Form)
- Implemented AuthGuard component for route protection
- Enhanced Header with user dropdown menu and logout functionality
- Updated Sidebar with user information display at bottom
- Added Team navigation item to sidebar
- Configured environment variables for API base URL

Technical Details:
- JWT token storage in localStorage with secure key names
- Automatic token refresh on 401 responses
- Request queueing during token refresh to prevent race conditions
- TypeScript strict typing throughout
- ESLint compliant code (fixed type safety issues)
- Proper error handling with user-friendly messages

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

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

lib/hooks/useAuth.ts

@@ -0,0 +1,110 @@
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
+import { apiClient, tokenManager } from '../api/client';
+import { API_ENDPOINTS } from '../api/config';
+import { useAuthStore } from '@/stores/authStore';
+import { useRouter } from 'next/navigation';
+
+interface LoginCredentials {
+  email: string;
+  password: string;
+}
+
+interface RegisterTenantData {
+  email: string;
+  password: string;
+  fullName: string;
+  tenantName: string;
+}
+
+export function useLogin() {
+  const setUser = useAuthStore((state) => state.setUser);
+  const router = useRouter();
+
+  return useMutation({
+    mutationFn: async (credentials: LoginCredentials) => {
+      const { data } = await apiClient.post(API_ENDPOINTS.LOGIN, credentials);
+      return data;
+    },
+    onSuccess: (data) => {
+      tokenManager.setAccessToken(data.accessToken);
+      tokenManager.setRefreshToken(data.refreshToken);
+
+      setUser({
+        id: data.user.id,
+        email: data.user.email,
+        fullName: data.user.fullName,
+        tenantId: data.user.tenantId,
+        tenantName: data.user.tenantName,
+        role: data.user.role,
+        isEmailVerified: data.user.isEmailVerified,
+      });
+
+      router.push('/dashboard');
+    },
+  });
+}
+
+export function useRegisterTenant() {
+  const router = useRouter();
+
+  return useMutation({
+    mutationFn: async (data: RegisterTenantData) => {
+      const response = await apiClient.post(
+        API_ENDPOINTS.REGISTER_TENANT,
+        data
+      );
+      return response.data;
+    },
+    onSuccess: () => {
+      router.push('/login?registered=true');
+    },
+  });
+}
+
+export function useLogout() {
+  const clearUser = useAuthStore((state) => state.clearUser);
+  const queryClient = useQueryClient();
+  const router = useRouter();
+
+  return useMutation({
+    mutationFn: async () => {
+      try {
+        await apiClient.post(API_ENDPOINTS.LOGOUT);
+      } catch {
+        // Ignore logout errors
+      }
+    },
+    onSuccess: () => {
+      tokenManager.clearTokens();
+      clearUser();
+      queryClient.clear();
+      router.push('/login');
+    },
+  });
+}
+
+export function useCurrentUser() {
+  const setUser = useAuthStore((state) => state.setUser);
+  const clearUser = useAuthStore((state) => state.clearUser);
+  const setLoading = useAuthStore((state) => state.setLoading);
+
+  return useQuery({
+    queryKey: ['currentUser'],
+    queryFn: async () => {
+      const { data } = await apiClient.get(API_ENDPOINTS.ME);
+      setUser(data);
+      setLoading(false);
+      return data;
+    },
+    enabled: !!tokenManager.getAccessToken(),
+    retry: false,
+    staleTime: 5 * 60 * 1000, // 5 minutes
+    refetchOnWindowFocus: false,
+    throwOnError: () => {
+      clearUser();
+      tokenManager.clearTokens();
+      setLoading(false);
+      return false;
+    },
+  });
+}