extension-features

Add a `features` array of strings under `contributes` in the extension's package.json. The extension loader reads it at activation and calls featureRegistry.registerFeatures, returning a Disposable that unregisters the feature automatically on deactivation.

Import the registeredFeatures store and check `$registeredFeatures.includes('feature-name')` with a $derived value. For imperative side effects, also listen on onDidChangeRegisteredFeatures and subscribe to the store inside onMount to catch both future changes and pre-existing state.

Listening only to onDidChangeRegisteredFeatures misses features registered before the component mounted. Combine the event listener with a registeredFeatures store subscription in onMount to sync the current state at mount time.

No manual cleanup is needed. The Disposable returned by registerFeatures is added to the extension's subscriptions, so the feature is unregistered automatically when the extension is deactivated.

The kube-context extension registers `kubernetes-contexts-manager`, which hides the built-in Kubernetes section in the Preferences navigation. PreferencesNavigation.svelte is the reference implementation for reacting to it.