PART 1: Created and implemented enums throughout the codebase to replace hardcoded status strings, improving type safety and reducing the risk of typos.

app/enums.py

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+from enum import Enum
+
+
+class NotificationStatus(Enum):
+    CREATED = "created"
+    PENDING = "pending"
+    SENDING = "sending"
+
+    DELIVERED = "delivered"
+    SENT = "sent"
+
+    FAILED = "failed"
+    TEMPORARY_FAILURE = "temporary-failure"
+    PERMANENT_FAILURE = "permanent-failure"
+    TECHNICAL_FAILURE = "technical-failure"
+    VALIDATION_FAILED = "validation-failed"
+    CANCELLED = "cancelled"
+
+
+class ApiKeyType(Enum):
+    NORMAL = "normal"
+    TEAM = "team"
+    TEST = "test"
+
+
+class JobStatus(Enum):
+    PENDING = "pending"
+    IN_PROGRESS = "in progress"
+    FINISHED = "finished"
+    SENDING_LIMITS_EXCEEDED = "sending limits exceeded"
+    SCHEDULED = "scheduled"
+    CANCELLED = "cancelled"
+    READY_TO_SEND = "ready to send"
+    SENT_TO_DVLA = "sent to dvla"
+
+
+class InvitedUserStatus(Enum):
+    ACCEPTED = "accepted"
+    CANCELLED = "cancelled"
+    EXPIRED = "expired"
+
+
+class InvitedOrgUserStatus(Enum):
+    ACCEPTED = "accepted"
+    CANCELLED = "cancelled"
+
+
+class VerificationStatus(Enum):
+    PENDING = "pending"
+    SUCCESS = "success"
+
+
+class HealthStatus(Enum):
+    OK = "ok"
+    ERROR = "error"
+
+
+class AuthType(Enum):
+    EMAIL_AUTH = "email_auth"
+    SMS_AUTH = "sms_auth"
+
+
+# TODO: UserRole enum
+# class UserRole(Enum):
+#     ADMIN = "admin"
+#     USER = "user"
+#     GUEST = "guest"
+
+
+# TODO: NotificationType enum
+# class NotificationType(Enum):
+#     EMAIL = "email"
+#     SMS = "sms"
+#     PUSH = "push"