Add Mob class extending Entity

src/mudlib/entity.py

@@ -14,3 +14,11 @@ class Entity:
     async def send(self, message: str) -> None:
         """Send a message to this entity. Base implementation is a no-op."""
         pass
+
+
+@dataclass
+class Mob(Entity):
+    """Represents a non-player character (NPC) in the world."""
+
+    description: str = ""
+    alive: bool = True