feat: implement user management system

- Add role field to UserProfile (superadmin/admin/trainer)
- Add role-based permission classes
- Create UserManagementViewSet with CRUD and password change
- Add API types and components for user management
- Create users management page in settings
- Only superadmins can manage users

backend/auth_app/serializers.py

@@ -1,6 +1,6 @@
 from rest_framework import serializers
 from django.contrib.auth.models import User
-from .models import UserPreferences
+from .models import UserPreferences, UserProfile
 
 
 class UserSerializer(serializers.ModelSerializer):
@@ -62,3 +62,51 @@ class UserPreferencesSerializer(serializers.ModelSerializer):
     class Meta:
         model = UserPreferences
         fields = '__all__'
+
+
+class UserListSerializer(serializers.ModelSerializer):
+    role = serializers.SerializerMethodField()
+    
+    class Meta:
+        model = User
+        fields = ['id', 'username', 'email', 'first_name', 'last_name', 'is_active', 'role', 'date_joined']
+    
+    def get_role(self, obj):
+        if hasattr(obj, 'profile'):
+            return obj.profile.role
+        return 'trainer'
+
+
+class UserCreateSerializer(serializers.ModelSerializer):
+    password = serializers.CharField(write_only=True)
+    role = serializers.ChoiceField(choices=UserProfile.ROLE_CHOICES, default='trainer')
+    
+    class Meta:
+        model = User
+        fields = ['id', 'username', 'email', 'first_name', 'last_name', 'password', 'role']
+    
+    def create(self, validated_data):
+        role = validated_data.pop('role', 'trainer')
+        user = User.objects.create_user(**validated_data)
+        UserProfile.objects.create(user=user, role=role)
+        return user
+
+
+class UserUpdateSerializer(serializers.ModelSerializer):
+    role = serializers.ChoiceField(choices=UserProfile.ROLE_CHOICES, required=False)
+    
+    class Meta:
+        model = User
+        fields = ['id', 'username', 'email', 'first_name', 'last_name', 'is_active', 'role']
+    
+    def update(self, instance, validated_data):
+        role = validated_data.pop('role', None)
+        user = super().update(instance, validated_data)
+        if role and hasattr(user, 'profile'):
+            user.profile.role = role
+            user.profile.save()
+        return user
+
+
+class PasswordChangeSerializer(serializers.Serializer):
+    password = serializers.CharField(write_only=True, required=True)