feat(clients): add clients app basic structure and endpoints

apps/clients/api/permissions.py

@@ -0,0 +1,22 @@
+from rest_framework import permissions
+from apps.workspaces.models import WorkspaceMembership
+
+
+class IsClientWorkspaceMember(permissions.BasePermission):
+    """
+    Allows access only to users who are active members of the workspace associated with the client.
+    """
+    message = "شما عضو فضای کاری این مشتری نیستید."
+
+    def has_object_permission(self, request, view, obj):
+        """
+        Validates if the user exists in the workspace memberships for the requested client's workspace.
+        """
+        if not request.user.is_authenticated:
+            return False
+            
+        return WorkspaceMembership.objects.filter(
+            workspace=obj.workspace,
+            user=request.user,
+            is_active=True
+        ).exists()