add admin user management: list and delete registered users

sentence_api/models.py

@@ -155,6 +155,19 @@ class AuthResponse(BaseModel):
     user: UserPublic
 
 
+class UserAdminItem(BaseModel):
+    id: str
+    username: str
+    nickname: str
+    phone: Optional[str] = None
+    created_at: datetime
+    enrollment_count: int = 0
+
+
+class UserAdminListResponse(BaseModel):
+    users: List[UserAdminItem]
+
+
 class CourseSummary(BaseModel):
     video_hash: str
     title: str