refactor: replace createProperty() override with standard decorator pattern

[piotrekwitkowski]

Lit 3 warns in dev mode:

Overriding ReactiveElement.createProperty() is deprecated. The override will not be called with standard decorators.

CsBaseElement.createProperty() auto-converts camelCase property names to kebab-case attributes. This works with legacy decorators but will break when migrating to standard decorators.

The override needs to be replaced — either by specifying attribute: 'kebab-name' explicitly in each @property() declaration, or by applying the conversion in a shared mixin/decorator wrapper.

Not urgent — legacy decorators still work. But blocks future migration to standard decorators.