CngxFilterEditorComponent

Contract every consumer-supplied custom editor component must satisfy when registered against CNGX_FILTER_EDITORS.

Shape mirrors Angular 21 Signal Forms' FormValueControl<T>: the required value is a ModelSignal so two-way binding wires through [(value)] without a ControlValueAccessor. The optional fieldDef, expression, and disabled inputs are projected by the filter-builder row when the editor is mounted; consumers declare only the inputs they care about.