Introduced a new "Receivers" panel in `EnvelopeSenderEditorPage` to manage receivers. Added a popup for adding receivers with validation, email suggestions, and caching for performance. Updated the layout to display receiver details and signature fields.
Injected `EnvelopeReceiverPageDataService` for receiver-related operations. Added a `ReceiverDraft` model and implemented methods for managing receivers. Enhanced CSS for the new UI elements and ensured responsiveness. Minor refactoring and cleanup included.