How do property descriptors, getters/setters, and Object.freeze/seal/preventExtensions work — and how do libraries use defineProperty for computed properties and API deprecation warnings?

Imagine you have a toy box with special rules: some toys can't be taken out, some can't be changed, and some have a magic button that shows a different toy when you press it. Property descriptors are like those rules for objects in JavaScript, letting you control who can see, change, or delete a property.