refactor: replace hardcoded user plan strings with CloudPlan enum (#27675)

api/enums/cloud_plan.py

@@ -0,0 +1,15 @@
+from enum import StrEnum, auto
+
+
+class CloudPlan(StrEnum):
+    """
+    Enum representing user plan types in the cloud platform.
+
+    SANDBOX: Free/default plan with limited features
+    PROFESSIONAL: Professional paid plan
+    TEAM: Team collaboration paid plan
+    """
+
+    SANDBOX = auto()
+    PROFESSIONAL = auto()
+    TEAM = auto()